Neurofibromatosis (NF1): Causes, Is It Contagious, Can It Be Cured? A Dermatologist Explains Which Lumps Can Be Removed and Which Must Not Be Touched
Neurofibromatosis type 1 (NF1), also called von Recklinghausen disease, is a genetic condition caused by a fault in the NF1 gene. It produces light brown birthmarks the colour of milky coffee, freckles in the armpits and groin, and many benign tumours of the nerve sheath under the skin. It is not contagious, it is not caused by germs, and it does not spread to other people through touch, shared meals or close contact.
It affects roughly 1 in 2,500–3,000 newborns of every ethnic background. Most people with NF1 live normal lives, but adult patients keep asking three questions in the consulting room: Can these lumps be removed? · Will I pass it to my child? · Which lumps should I be afraid of? This article answers all three in plain language, and says clearly which lumps can be removed safely and which must not be touched and need to be checked urgently.
What is NF1, and why is it called “hundred thousand knots”?
The Thai name “Thao Saen Pom” comes from a folk-tale character whose body was covered in knots and bumps, so he was called “Saen Pom” (hundred thousand knots). Thai people borrowed the name for the condition that causes many small lumps on the skin, from a time when the cause was unknown. The name has stuck, but doctors use neurofibromatosis type 1 (NF1) or von Recklinghausen disease because it is more precise and does not stigmatise patients.
The condition is a fault in a single gene that shows up in many body systems, from the skin, eyes, bones and blood vessels to the nervous system. Severity varies widely from person to person, even within one family. Some people have only a few birthmarks and freckles for life, while others have hundreds of lumps plus problems in other systems, so nobody can tell from a parent's appearance whether a child will be mildly or severely affected.
It is not NF2, a separate condition caused by a different gene, which produces tumours on both hearing nerves and almost no skin signs.
What causes NF1?
Cause A mutation in the NF1 gene on chromosome 17. This gene makes a protein called neurofibromin, which acts as a brake that stops cells from dividing too much. When the gene is faulty the brake fails, and cells in the nerve sheaths divide into benign tumours anywhere in the body.
Inherited or new About half of patients inherit the faulty gene from a parent who has the condition. The other half arise from a new mutation in the person themselves (de novo mutation) at the embryo stage, with no affected parent. So having no one else in the family with it does not mean it is not NF1.
Inheritance pattern It is autosomal dominant, meaning that one faulty copy out of two is enough to cause the condition, and an affected person has a 50% chance of passing it to each child, boy or girl.
What does not cause it NF1 is not caused by food, anything the mother did during pregnancy, germs, or contact with other patients.
Is NF1 contagious?
Not contagious whether through skin contact, touching the lumps, sharing belongings, eating together, sexual contact or living in the same house, because no germ is involved. The only thing that can be “passed on” is the gene, from parent to child at conception.
This matters more than it may seem, because many patients are excluded from workplaces, swimming pools or barber shops out of fear of catching it, when living alongside a patient carries no risk at all for the people around them.
The 7 diagnostic criteria in plain language
Doctors worldwide use criteria set by the US National Institutes of Health (NIH), most recently updated in 2021. A diagnosis needs at least 2 of the following 7.
Six or more café-au-lait spots larger than 5 millimetres in children before puberty, or larger than 15 millimetres after puberty.
Freckling in the armpits or groin small brown spots 1–3 millimetres across in areas the sun does not reach.
Two or more neurofibromas of any type, or just 1 plexiform neurofibroma.
A tumour of the optic nerve pathway (optic pathway glioma).
Two or more Lisch nodules in the iris tiny brown bumps on the iris that an eye doctor finds with a microscope and that do not affect vision.
A characteristic bone abnormality such as thinning of the bone beside the eye socket (sphenoid dysplasia) or a bowed shin bone that fractures and does not heal.
A parent, sibling or child with NF1 by the criteria above.
The 2021 criteria add finding a faulty NF1 gene in the blood as another item, and require that if only café-au-lait spots and freckling are present, at least one of them must appear on both sides of the body, to separate NF1 from conditions with similar birthmarks.
In practice an adult with several soft lumps together with café-au-lait spots or armpit freckles can usually be diagnosed by a dermatologist from the physical examination alone. Genetic testing is used when the signs do not yet meet the criteria, in young children, or when planning a pregnancy.
Café-au-lait spots (often the first sign, before any lumps)
Appearance Light brown, flat, level with the skin, with a clear edge and an even colour like milky coffee. Oval or irregular, from a few millimetres to several centimetres, and can occur anywhere except the scalp, palms and soles.
Cause The pigment cells in that area are driven by the faulty NF1 gene to make more pigment than normal. It is not a tumour and does not turn into cancer.
Urgency Not urgent. One or two café-au-lait spots occur in 10–20% of the general population and do not mean the condition is present. What counts is having 6 or more that also meet the size criteria.
When to see a doctor A child with 6 café-au-lait spots, or spots that keep increasing in the first 2 years of life, should see a paediatrician or dermatologist to count and measure them and plan an eye examination before age 6. Details for parents are in Café-au-lait spots in children and NF1.
In adults café-au-lait spots may fade a little but do not disappear, and they need no treatment unless you want to lighten them for cosmetic reasons, in which case results are uncertain and the spots can darken again.
Armpit and groin freckling (Crowe sign)
Appearance Small brown spots 1–3 millimetres across, clustered in skin folds the sun does not reach: the armpits, groin, under the breasts, around the neck and around the mouth. Unlike ordinary freckles, which appear only on sun-exposed skin.
Cause The same mechanism as café-au-lait spots: extra pigment produced because of the faulty gene.
Urgency Not urgent and needs no treatment, but it is very valuable for diagnosis because it is found in about 70–90% of people with NF1 and is almost never seen in other conditions. It usually appears at age 3–5, later than café-au-lait spots.
When to see a doctor When it appears together with several café-au-lait spots, even before any lumps appear, because that already meets 2 diagnostic criteria.
Skin lumps: cutaneous neurofibromas
These are the “knots” that give the condition its name, and the thing most adults worry about most.
Appearance Soft, smooth lumps, skin-coloured or slightly pink-purple, from 2–3 millimetres to 2–3 centimetres. Some are dome-shaped and some hang on a stalk like a skin tag. When pressed with a fingertip the lump sinks into the skin like a button going into a buttonhole, then pops back when released, called the buttonhole sign, which helps tell it apart from other types of lump. Some itch or are mildly painful when rubbed.
Cause Small nerve sheath cells under the skin multiply into a lump, a benign tumour. This type of lump does not turn into cancer and does not spread to internal organs.
When they appear Most start in the teenage years and increase in number and size throughout life, often noticeably during pregnancy because hormones stimulate growth. Some adults have only a few, others hundreds to thousands.
Urgency Low. These lumps are not life-threatening. The main problems are irritation, friction and the effect on confidence.
When to see a doctor When a lump is persistently painful, is rubbed raw and often ulcerated, bleeds, grows unusually fast, or when you want to discuss removal.
Another type lies deeper, the subcutaneous neurofibroma, which feels firmer, lies along the line of a nerve, and may cause a tingling or numb feeling along the nerve when pressed. This type needs closer follow-up than the first.
Plexiform neurofibromas (the lumps to watch)
Appearance Completely different from the small lumps above. A large lump with an unclear edge, soft and springy, feeling like a bag of worms with several cords tangled inside. The skin over it is often darker than normal with more hair than the surrounding skin. It can make the arm, leg or side of the face larger than the other side.
Cause A tumour growing along the branches of a large nerve and spreading into the surrounding tissue, so its edge is unclear and it is hard to remove completely. It occurs in about 30–50% of people with NF1, mostly present from birth, though it may only become obvious as the person grows, and it often enlarges quickly from childhood to the teenage years.
Urgency Moderate to high, because it is the main type of lump in NF1 that can turn into cancer, and it can press on nerves, the airway or bone depending on where it lies.
When to see a doctor Every plexiform lump should have a regular doctor following it, and you must see a doctor immediately if any of the warning signs in the next section appear.
Warning signs: which lumps must not be touched yourself and need urgent checking
Plexiform lumps, or deep lumps along a nerve, can change into a cancer of the nerve sheath (malignant peripheral nerve sheath tumour, MPNST), with a lifetime risk in NF1 of about 8–13%. The most common age is 20–40. This cancer responds best to treatment when found early, so you need to know these warning signs.
Fast growth A lump that stayed still for a long time and then clearly enlarges within a few weeks to a few months.
Persistent pain Especially pain at night that wakes you, or pain without any pressure or knock. Most ordinary lumps do not hurt.
Change in texture From soft and springy to hard, or hard in one part inside an existing lump.
Numbness, weakness or an arm or leg that no longer works as before in the area supplied by that nerve.
A new deep lump A new lump felt in the upper arm, thigh, hip or back, which are common sites for MPNST.
If any one of these is present, see a doctor within 1–2 weeks. The doctor will order an MRI or PET scan and a biopsy when needed. Do not squeeze it, and do not let anyone cut out a lump like this without imaging first, because incomplete, unplanned surgery can spread cancer cells and make later treatment harder.
Small, soft lumps on the skin that sink in when pressed, do not hurt and do not grow fast are in the safe group, with no need to worry about cancer.
Beyond the skin: eyes, bones, blood pressure and learning
NF1 is not only skin deep. Patients and families should know the common problems in other systems, because many can be found and managed if you know what to look for.
Eyes Lisch nodules in the iris occur in over 90% of adults but do not affect vision and need no treatment. What needs watching is the optic pathway glioma, found in about 15–20% of children, mostly before age 6–7. Some cases cause blurred vision, a bulging eye or early puberty. Children therefore need an eye examination by an ophthalmologist every year until age 8–10. New optic pathway tumours in adults are very rare.
Bones Scoliosis occurs in about 10–30%, usually starting at age 6–10, and some curves progress fast enough to need surgery. Less common problems are a bowed shin bone from early childhood that fractures and does not heal, short stature, a larger than average head, and low bone density in adults.
Blood pressure People with NF1 develop high blood pressure more often than others. Most is ordinary high blood pressure, but two treatable causes must be considered: narrowing of the kidney artery in young patients, and pheochromocytoma (an adrenal gland tumour), found in about 1–5%, which causes episodes of high blood pressure, palpitations, sweating and headache. Screening should be considered before major surgery or before pregnancy.
Brain and learning About half of children with NF1 have specific learning difficulties such as slow reading, slow arithmetic or attention problems, even though overall intelligence is in the normal range. Early assessment and support let the child keep up with classmates. Some adults get migraine headaches more often than others.
Other cancers Women with NF1 have a higher risk of breast cancer before age 50 than the general population, so international guidelines recommend starting breast screening at age 30, earlier than for others. Tumours of the digestive tract (GIST) and some childhood leukaemias also occur, though not often.
At what age does NF1 appear? A timeline by age
The faulty gene is there from birth, but each sign appears gradually with age. This is why young children are often diagnosed late, and why some adults only find out in their 30s.
Birth to 2 years Café-au-lait spots appear and increase in number. Most children with NF1 have all 6 spots before age 2. Some plexiform lumps can be seen from birth.
3–5 years Armpit and groin freckling begins, the second criterion that often allows a diagnosis at this age.
Before 6–7 years The risk period for optic pathway glioma, so yearly eye checks are needed.
6–10 years Lisch nodules in the iris start to be found, scoliosis starts to be noticed, and learning problems become clearer once at school.
Teenage years (10–18) Neurofibromas begin to appear on the skin, and plexiform lumps grow fast in this period.
20–40 years The number of lumps keeps increasing, especially during pregnancy, and this is the age range when MPNST needs the closest watch.
30 years and over (women) Start breast cancer screening.
40 years and over Lumps may still increase slowly. The main issues are blood pressure and quality of life with a large number of lumps.
Adults diagnosed only later in life are mostly people whose signs were mild or overlooked in childhood. It does not mean the condition has only just begun.
Can NF1 be cured? What can be done?
The straight answer is that there is no cure yet, because the faulty gene is in every cell of the body. Current treatment is therefore to manage each problem as it arises and to monitor so that treatable problems are caught in time. Most patients work, raise families and live a lifespan close to that of the general population.
What can actually be done today
Skin lumps Can be removed or flattened one at a time when they interfere with daily life.
Plexiform lumps Surgery by a specialist surgeon when it is feasible, and a newer class of drug for lumps that cannot be operated on.
Eyes, bones, blood pressure Scheduled checks and treatment when problems are found, such as blood pressure medication or spinal surgery.
Learning Assessment and a support plan for children from before they start school.
Mind and social life Talking with a doctor, a psychologist or a patient group helps a great deal, because part of the burden of this condition comes from how others look at patients, not only from the condition itself.
There is no drug, cream, herbal remedy or supplement that makes the lumps disappear. Be wary of any advertisement that claims so.
Can the lumps be removed? When should they be?
Yes, and it is the treatment adults ask about most, but you must first understand that removal does not stop the condition. New lumps can keep appearing, so removal solves problems one spot at a time and is not a treatment of the condition itself.
Lumps suitable for removal Skin lumps that hurt, itch, or are rubbed by clothing or bra straps, lumps on the face or in places that affect confidence, or lumps on a stalk that twist and hurt.
Methods used Depend on size, number and location.
Minor surgery The lump is cut out and the wound stitched closed, under local anaesthetic. Suitable for larger lumps or lumps that need to be sent for biopsy. The result is permanent for that lump, but leaves a small scar in proportion to the lump.
Carbon dioxide laser treatment or electrocautery. Suitable for many small lumps in a single session. Wounds heal faster, but many spots need wound care at once, and lumps that still have a deep part can come back.
What to know before removal
Every method leaves some mark, such as a flat scar, a pale mark or a darker mark, depending on skin tone and location.
A lump that is removed completely does not return in the same place, but new lumps can appear next to it.
Skin lumps do not need to be removed to prevent cancer, because they do not become cancer. Remove them only when they cause trouble.
Any lump with a suspicious appearance should always be sent for a pathology biopsy.
Plexiform lumps and deep lumps must be assessed by a surgeon experienced with NF1 together with MRI imaging, not removed in an ordinary dermatology clinic.
A newer class of drug that shrinks plexiform lumps
The major advance in this condition over the past decade is the class of drugs called MEK inhibitors, which switch off the growth signal that the NF1 gene can no longer control. The first drug in this class was approved by the US Food and Drug Administration in 2020 for children aged 2 years and over with symptomatic plexiform neurofibromas that cannot be operated on. In the main study about 70% of children had their lumps shrink by 20% or more, with improvement in pain and in how the affected body part worked. In 2025 the approved use was extended to adults in some countries.
What to understand correctly
This drug is used for plexiform lumps only. It does not make the small skin lumps go away.
It is taken by mouth, must be continued for years, and the lumps may grow back when the drug is stopped.
It has common side effects such as an acne-like rash, diarrhoea and inflamed nail folds, and needs periodic heart and eye checks.
Use of the drug must be under a specialist doctor in a hospital with an NF1 care team. This article gives information so patients know the option exists and can discuss it with their own doctor. It is not a service of the dermatology clinic.
Family planning: if you have NF1 and want children
A 50% chance of passing it on in each pregnancy whether the father or the mother is affected, and whichever sex the child is. Having a first child without the condition does not reduce the chance for the next one.
Severity cannot be predicted A parent with mild signs may have a child with severe signs and the reverse, because the same gene shows itself differently in each person.
Options that really exist You should see a clinical geneticist before pregnancy, who will explain these options.
Test the patient's own gene first to learn which mutation this family has. This step is needed before a child can be tested.
Preimplantation genetic testing (PGT-M) together with IVF, to choose an embryo without the faulty gene for transfer.
Prenatal diagnostic testing by chorionic villus sampling at 10–13 weeks of pregnancy, or amniocentesis at 15–20 weeks.
Natural pregnancy and testing the baby after birth which many families choose, because most patients have a good quality of life.
During pregnancy Skin lumps often increase in number and size. Blood pressure must be measured at every antenatal visit, and you should tell the obstetrician about NF1 at the very first visit.
Special case People whose signs are limited to one part of the body (segmental NF1) have the faulty gene in only some cells. The chance of passing it on is lower than 50% but not zero, and must be assessed individually.
Follow-up: a yearly checklist for adults
People with NF1 who do not have severe problems should see a doctor at least once a year, and each visit should cover the following.
Whole-body skin examination noting any lump that is growing fast or changing, especially plexiform lumps.
Blood pressure at every visit. If it is high in a young person or comes in episodes, look for a cause.
Ask about new pain, numbness or weakness in the past year.
Eye examination in adults when there are symptoms, and every year in children until age 8–10.
Spine check in teenagers who are still growing.
Women aged 30 and over yearly breast cancer screening.
One whole-body MRI at the transition to adulthood, to look for internal lumps that cannot be seen from outside. Guidelines in some countries have begun to recommend this.
Before pregnancy or major surgery consider screening for an adrenal tumour.
Review mental health and work because stress and stigma are real problems that a doctor can help find a way through.
Patients with plexiform lumps, an eye tumour or neurological symptoms need more frequent follow-up as set by a specialist doctor.
Telling it apart from skin tags, fatty lumps and similar conditions
Many lumps on the skin are not always NF1, and adults with only a few lumps often worry more than they need to.
Skin tags are small stalked lumps on the neck, armpits and groin, with wrinkled brown skin, no buttonhole sign and no café-au-lait spots. They are very common in the general population, especially in people who are overweight. Read more in What causes skin tags.
Fatty lumps and cysts A fatty lump (lipoma) is soft, deeper, larger and moves about under the skin, while a cyst usually has a central pore with white material inside. Neither sinks in when pressed. Read how to tell them apart in What causes lumps under the skin.
A single neurofibroma Anyone can have a single neurofibroma without having NF1. With one lump, no café-au-lait spots, no fold freckling and no family history, the criteria are not met.
Legius syndrome has café-au-lait spots and fold freckling like NF1 but no lumps, no Lisch nodules and no tumour risk. It is told apart by gene testing. This is why the 2021 criteria are careful about people who have only birthmarks and freckles.
NF2 and schwannomatosis are different conditions that also have lumps along nerves, but usually no café-au-lait spots or freckles, and hearing problems or chronic pain are the main symptoms.
Other skin conditions that cause lumps or many birthmarks are covered in the clinic's Skin Conditions section.
When to see a dermatologist
You have several soft lumps on the skin together with café-au-lait spots or fold freckling, and have never been diagnosed.
An existing lump grows fast, hurts, becomes harder, or comes with numbness or weakness. Be seen within 1–2 weeks.
A lump is rubbed until it is ulcerated, bleeds, or is repeatedly infected.
You want to discuss removing lumps that bother you, or want an opinion on which lumps should be removed and which referred on.
You are planning a pregnancy, or have a child with several café-au-lait spots.
You have not had a yearly check for more than 2 years.
Diagnosis and treatment planning must be done by a doctor after a real examination. A dermatologist will coordinate with an eye doctor, surgeon, physician and geneticist as each person needs.
Short summary
Thao Saen Pom = NF1 A genetic condition from the NF1 gene. Half is inherited from a parent and half arises newly in the person.
Not contagious No germ is involved. It can only pass on through genes to a child, with a 50% chance per pregnancy.
Diagnosed by 2 of 7 criteria 6 café-au-lait spots, fold freckling, 2 lumps, eye tumour, Lisch nodules, bone abnormality, first-degree relative.
Small soft lumps on the skin that sink in when pressed = safe Can be removed when they bother you. They do not become cancer.
A plexiform or deep lump that grows fast, hurts, hardens or causes numbness = do not touch it yourself Needs an MRI within 1–2 weeks because of the 8–13% lifetime MPNST risk.
Not curable but manageable A yearly check, blood pressure at every visit, breast screening for women from age 30, and a newer class of drug for plexiform lumps that cannot be operated on.
Frequently asked questions
Can NF1 be cured?
There is no cure yet, because the cause is the faulty NF1 gene found in every cell of the body, but the condition can be managed well. Most patients work, raise families and live a lifespan close to that of the general population. Treatment has three parts: removing or flattening skin lumps one at a time when they bother you, surgery or MEK inhibitor drugs for symptomatic plexiform lumps, and yearly follow-up to catch treatable problems such as high blood pressure, scoliosis and lumps turning cancerous in time. There is no drug, cream or herbal remedy that makes all the lumps disappear.
What are the symptoms of NF1 in children?
Young children have almost no lumps. The first sign is 6 or more light brown café-au-lait spots that appear and increase in the first 2 years, followed by small freckles in the armpits and groin at age 3–5. Some have a larger than average head, short stature or a bowed shin bone. Problems to watch are optic pathway glioma, found in 15–20% and mostly before age 6–7, which is why yearly eye checks are needed, and learning problems or attention problems, found in about half. Scoliosis starts to be noticed in primary school age, and skin lumps usually start in the teenage years.
Is NF1 contagious?
No, whether through touching the skin, touching the lumps, sharing belongings, eating together, swimming in the same pool or sexual contact, because the condition is not caused by any germ but by the faulty NF1 gene in the patient's own body. The only way it can be “passed on” is from parent to child at conception, with a 50% chance in each pregnancy. Living in the same house, working together or caring closely for a patient carries no risk at all for the people around them.
What is neurofibromatosis type 1?
It is the medical name for Thao Saen Pom, known as neurofibromatosis type 1 or NF1. It is a dominantly inherited genetic condition caused by a mutation in the NF1 gene on chromosome 17, which makes nerve sheath cells divide into many benign tumours, together with café-au-lait spots, fold freckling and bumps on the iris. It occurs in about 1 in 3,000 newborns, half inherited from a parent and half from a new mutation. It is a different condition from NF2, which is caused by another gene and mainly produces tumours of the hearing nerve.
What are the first symptoms of NF1?
The first sign, found in almost every case, is café-au-lait spots: light brown, flat spots with clear edges, larger than 5 millimetres, 6 or more in number, usually appearing from birth to 2 years. In an adult who has only just noticed it, the symptom that brings them to a doctor is usually small skin-coloured soft lumps that have slowly increased in number since the teenage years and sink in when pressed, together with small freckles in the armpits or groin that have been there for a long time without being noticed. If you have both of these, see a dermatologist to confirm the diagnosis and start follow-up.
At what age does NF1 appear?
The faulty gene is there from birth, but signs appear gradually with age. Café-au-lait spots appear from birth to 2 years, fold freckling at 3–5 years, Lisch nodules in the iris at 6–10 years, and skin lumps start in the teenage years and then increase for life, especially during pregnancy. Plexiform lumps are often present from birth but grow noticeably in childhood to the teenage years. Most children are diagnosed before age 8, while adults first diagnosed at 20–40 are usually people whose childhood signs were mild enough to be overlooked. It does not mean the condition has only just begun.
The information in this article is for general understanding and is not a diagnosis or individual treatment. Assessment of lumps and treatment planning should be done by a doctor.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed September 7, 2026
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