Psoriasis: Causes, Early Symptoms, How to Tell It Apart from Seborrheic Dermatitis and Fungal Infection, and Treatment for Long-Term Remission

3 days ago

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Psoriasis is a chronic inflammatory skin disease caused by an overactive immune system. It is not contagious, and it is not caused by poor hygiene or infection. The heart of care is to get the diagnosis right first and then choose treatment that suits the severity, because rashes that look like psoriasis can come from many conditions, and using the wrong kind of cream at home, especially strong steroids, can make the disease harder to control in the long run.

This article was written by a dermatologist to explain what psoriasis is, what causes it, what the early symptoms look like, and how to tell it apart from dandruff, seborrheic dermatitis and fungal infection. It also covers evidence-based treatment and common food myths.

What is psoriasis?

Psoriasis is a condition in which the immune system drives skin cells to multiply and shed several times faster than normal. Skin normally renews itself in about 28 days, but in people with psoriasis this can drop to just 3–5 days. Immature cells pile up into thick, red patches covered with silvery-white scales, which is where the condition gets its name.

Key points to understand from the start:

Not contagious — touching, close contact, sharing belongings or swimming together does not spread it.
Not a fungus and not an ordinary allergy — it is an immune system disease with its own distinct features.
A chronic disease that can be controlled, but there is no cure yet — the realistic goal is remission and preventing flare-ups.
Not skin cancer — this is a common misunderstanding. Psoriasis does not turn into cancer.

What causes psoriasis?

The underlying cause is a fault in the T-cell part of the immune system that triggers inflammation and speeds up skin cell growth, combined with genes that make some people more prone to the disease. People with a parent or close relative who has psoriasis have a higher risk, but not everyone with a family history will develop it.

Although genetics and immunity form the foundation, triggers are often what set off a first outbreak or a flare. They include:

Stress, both physical and emotional, is the most common trigger.
Infections, especially streptococcal throat infections, which often trigger guttate psoriasis in children and teenagers.
Skin injury such as scratches, cuts, tattoos or sunburn. Psoriasis often appears right at the site of injury, a response called the Koebner phenomenon.
Certain medicines such as beta-blockers, lithium, antimalarial drugs, and suddenly stopping oral steroids.
Smoking and alcohol both trigger the disease and make it harder to control.
Cold, dry weather. Dry skin tends to make the rash worse, while gentle sunlight helps some people.

What do early psoriasis symptoms look like?

The early sign to look for is a red rash with well-defined edges, slightly raised, covered by silvery-white scales. When the scales are gently scraped off, tiny pinpoint spots of bleeding may appear underneath (Auspitz sign), a feature that helps tell psoriasis apart from other skin conditions.

Features often seen in the early stage:

The rash starts as small spots and gradually spreads and thickens.
Common sites are the elbows, knees, scalp, hairline, lower back and the cleft between the buttocks, often on both sides in a symmetrical pattern.
Itching is common but not always present.
The skin in the rash is dry, cracked and sometimes painful or bleeding.
Nail changes such as tiny pits like pinpricks, thickened nails or nails that lift off can also be an early sign.

If you have a chronic red, scaly rash in these areas that does not clear with ordinary creams and comes and goes, you should see a dermatologist for a clear diagnosis.

What types of psoriasis are there?

Psoriasis comes in several forms. Identifying the type matters because each has a different severity and treatment approach:

Plaque psoriasis — the most common type, affecting about 8 in 10 patients, with thick red patches and silvery scales on the elbows, knees, scalp and trunk.
Guttate psoriasis — small teardrop-like spots spread across the body, often after a throat infection, and common in children and teenagers.
Inverse psoriasis — smooth, shiny red patches in skin folds such as the armpits, under the breasts and the groin. Scales are usually absent because these areas are moist, so it is often mistaken for a fungal infection.
Scalp psoriasis — thick scaly patches on the scalp that often extend past the hairline onto the forehead and behind the ears.
Nail psoriasis — nails with pits, thickening, discoloration or lifting.
Pustular psoriasis — pus-filled bumps on red skin. If it spreads over the whole body with fever, it is a severe condition that needs a doctor immediately.
Erythrodermic psoriasis — red, peeling skin over nearly the whole body. This is a life-threatening emergency that needs hospital treatment.

How is scalp psoriasis different from dandruff and seborrheic dermatitis?

This is where people in Thailand are most often confused, because all three conditions cause scaling and itching on the scalp, yet they are different diseases treated with different medicines.

Ordinary dandruff — fine white or yellow flakes, with a scalp that is not very red or thick and only mild itching. It usually improves with anti-dandruff shampoo.
Seborrheic dermatitis — greasy yellow scales, with redness that is not distinct and edges that are not sharp. It commonly affects the scalp, the sides of the nose, the eyebrows and the forehead.
Scalp psoriasis — thick patches that are clearly red with sharp edges and thick silvery-white scales. They are usually thicker and extend past the hairline onto the forehead and behind the ears with a clear border.

Because seborrheic dermatitis and psoriasis can occur together and are sometimes hard to tell apart by eye, an examination by a dermatologist together with dermoscopy (skin microscope) gives a more accurate diagnosis than guessing. To learn more about similar conditions, you can also read our article on seborrheic dermatitis and dandruff.

Is psoriasis contagious? Is it cancer?

These two questions are very common, and the answers are clear:

Not contagious — psoriasis comes from the patient's own immune system, not from germs. Touching, hugging, shaking hands or sharing belongings does not spread it. People with psoriasis can live, work and socialize normally.
Not cancer, and does not turn into cancer — psoriasis is chronic inflammation, not a tumor. However, some chronic rashes can look similar, so an examination by a doctor can confirm the diagnosis and rule out skin cancer.

Psoriasis is not just a skin disease

A point often overlooked is that psoriasis involves inflammation throughout the body and is not limited to the skin. Some patients develop related conditions, which is why care should look at the whole person and not just apply cream until the rash clears.

Psoriatic arthritis — about 1 in 3 patients may have pain and swelling in the joints, fingers and toes, or lower back pain. Left untreated, it can cause permanent joint damage, so tell your doctor if you have joint pain as well.
Metabolic and heart disease — psoriasis is linked to a higher risk of diabetes, high blood pressure, high cholesterol and heart disease. Managing weight and heart health is part of treatment.
Effects on mental health — a visible rash can affect confidence and may lead to stress or depression, which in turn can trigger the disease again.

How do doctors diagnose psoriasis?

Dermatologists can usually diagnose psoriasis from the look and location of the rash and the patient's history, with extra tests when needed:

Examining the body and rash — checking the patches, their edges, the scales and symmetrical locations, along with the nails and scalp.
Dermoscopy — shows the blood vessel pattern typical of psoriasis and helps separate it better from seborrheic dermatitis and fungal infection.
Skin biopsy — used in unclear cases to confirm the diagnosis and rule out other conditions.
Assessing severity and joint involvement — to plan treatment that suits the area affected and the impact on daily life.

How is psoriasis treated to reach remission?

The doctor chooses treatment based on severity, rash location and other health conditions, assessing the area of the rash relative to total body surface (one patient's palm is about 1%) and the effect on daily life. The current goal is to reduce the rash by at least 75% (PASI 75) or to leave less than 1–3% of the skin affected, not merely to get "a bit better".

Mild rash: less than 3% of the skin and not in difficult locations → start with topical treatment.
Moderate to severe rash: more than 10% of the skin, or a smaller rash on the scalp, face, palms and soles, genitals or nails, or with arthritis → add phototherapy, oral medicine or injections.

Mild rash: topical treatment

Very strong steroids such as clobetasol propionate 0.05% or betamethasone dipropionate 0.05%: applied to thick patches on the trunk, limbs and scalp once or twice a day for no more than 2–4 weeks continuously, then reduced to weekends only to keep flare-ups under control.
Calcipotriol 0.005% (50 micrograms/gram): a vitamin D derivative applied once or twice a day, no more than 100 grams per week. It works better combined with a steroid than used alone. A calcipotriol and betamethasone combination applied once a day for 4 weeks is the standard for trunk and scalp patches.
Face, skin folds and genitals: the skin is thin, so a mild steroid such as hydrocortisone 1% is used for short periods, or a calcineurin inhibitor such as tacrolimus ointment 0.03–0.1% twice a day.
Very thick scales: salicylic acid 3–6% is used first to dissolve the scales so the medicine absorbs better. On the scalp, use a liquid steroid or clobetasol shampoo left on for 15 minutes and then rinsed off.

Checking progress: you should see the rash clearly thinner within 2–4 weeks. If the rash has improved by less than half after 8 full weeks of use, go back to the doctor to step up treatment. Details on each group of topicals are in Psoriasis creams: types, strengths and how long to use them

Moderate rash: narrowband ultraviolet B phototherapy (NB-UVB 311 nm)

Treatment is given 2–3 times a week. Most people start to see results after 15–20 sessions, and a course takes about 20–30 sessions. A side effect is skin redness similar to sunburn. The drawback is the need to attend regularly, and you should not use a tanning bed or sunbathe on your own instead, because that gives UVA rays that do not work for the disease and raise the risk of skin cancer.

Moderate to severe rash: oral medicines

Methotrexate 7.5–25 mg taken "once a week" only: never take it daily, because it can cause life-threatening bone marrow toxicity. It is taken with folic acid 5 mg once a week on a different day. Blood tests for blood counts, liver and kidney are needed before starting and every 1–3 months. Avoid alcohol, and use contraception while on the drug. Results appear in 8–12 weeks. Read more in Methotrexate for psoriasis: dosage and monitoring
Ciclosporin 2.5–5 mg/kg/day divided into 2 doses: it works fast, with results in 4–6 weeks, and suits severe flare-ups. It is used short term, usually no more than 1 year, because it affects the kidneys and blood pressure, so blood pressure and kidney function must be checked regularly.
Acitretin 25–50 mg/day: suits pustular psoriasis and psoriasis of the palms and soles. It can cause dry lips and high blood fats, and it causes birth defects: women must not be pregnant during treatment and for 3 years after stopping.
Apremilast 30 mg twice a day: start at a low dose and increase over the first 6 days. Common side effects are diarrhea, nausea, headache and weight loss. It does not need frequent blood monitoring, but it works less well than biologic injections.

Severe rash or arthritis: biologic injections (Biologics)

These are injections under the skin that block specific inflammatory signals. They are divided into TNF-alpha inhibitors (such as adalimumab), interleukin-17 inhibitors (such as secukinumab, ixekizumab) and interleukin-23 inhibitors (such as guselkumab, risankizumab). They are given every 2–12 weeks depending on the drug. Most patients see the rash reduce by at least 75% within 12–16 weeks. Before starting, screening for latent tuberculosis and hepatitis B and C is required. They are usually used in people who do not respond to, or cannot use, oral medicines. If you also have joint pain, some groups help both skin and joints. For joint symptoms that need prompt checking, see Psoriatic arthritis: warning signs before joints are permanently damaged

What not to use: oral or intramuscular steroids, because when the drug is stopped the rash often returns worse than before and may turn into whole-body pustular psoriasis.

Signs that treatment is working: the rash is thinner, scaling is reduced, the area of the rash has shrunk by at least 75% within 3–4 months, itching has eased, and sleep is better. If this goal is not reached, the doctor will adjust the dose or change the type of medicine. The choice of medicine and dose is always the doctor's decision after examination and blood tests.

With current medicines, most patients can get the rash to settle until it is barely visible and live normally, although ongoing care is still needed.

Where should I go for care, and what needs follow-up?

Dermatologist: diagnoses and separates psoriasis from seborrheic dermatitis, fungal infection and allergic rashes, plans topical treatment, and assesses whether you meet the criteria for oral medicine or injections.
Facilities with an NB-UVB phototherapy machine: for people who need phototherapy 2–3 times a week, choose a place that is easy to travel to.
Hospitals with dermatologists who can prescribe biologic injections: for severe rashes or those that do not respond to oral medicines.
Rheumatologist: when the finger joints are swollen, there is back pain in the morning, or joint stiffness lasts longer than 30 minutes.

Yearly check-ups: people with moderate to severe psoriasis have a higher risk of heart and blood vessel disease than the general population. Check blood pressure, weight and waist, and blood sugar and cholesterol at least once a year, check liver function when using oral medicines, and watch for low mood, which is common alongside psoriasis.

Why does the cream not work, and what to watch out for with steroids

Many patients feel that the cream never seems to clear the rash. Common reasons include:

Wrong diagnosis from the start — assuming it is a fungus or seborrheic dermatitis and buying medicine to use at home, so the treatment does not match the disease.
Not finishing the medicine or not using it continuously — stopping as soon as the rash improves, which causes it to flare again.
Stopping steroids suddenly — especially oral steroids, or strong topical steroids used over large areas for a long time. Stopping on your own can cause a severe rebound flare, and sometimes it turns into the more dangerous pustular type.

Important warning: do not buy packaged medicine sets, herbal remedies or creams that claim to cure psoriasis completely, because many contain undeclared strong steroids, so you seem to improve at first and then flare badly later. Steroid adjustments should always be made under a doctor's care.

What foods should I avoid with psoriasis? Can I eat eggs? Do herbs really help?

Food is a question that worries patients a lot, and there is a lot of false information around. The truth according to current evidence is:

There is no specific forbidden food proven to make psoriasis clear or flare in everyone — including eggs, which many people worry about. There is no evidence that people with typical psoriasis need to give them up.
What has reasonable evidence of benefit is controlling weight, cutting down alcohol and quitting smoking, because all three are linked to more flare-ups and a poorer response to medicine.
A Mediterranean-style diet rich in vegetables, fruit, fish and healthy fats may help reduce overall inflammation in the body, but it is a supplement and not a replacement for medicine.
Herbs and products claiming a complete cure, such as decoctions, herbal brews or various extracts, do not have strong enough medical evidence, and some may affect the liver or be contaminated with steroids. Always talk to a doctor before using them.

Put simply, eating a balanced diet and looking after your overall health is beneficial, but there is no magic menu that makes psoriasis go away on its own.

Warning signs that need a doctor soon

Most psoriasis is not an emergency, but a few situations need prompt medical attention:

Red, peeling skin over nearly the whole body with chills or fever (suspected erythrodermic psoriasis)
Pus-filled bumps all over the body with fever and feeling very unwell (suspected severe pustular psoriasis)
Joint pain and swelling that makes movement difficult, which may be psoriatic arthritis that needs early treatment
A rash that spreads unusually fast after stopping steroids or after starting a new medicine
A secondarily infected rash with pus, pain, swelling, redness and warmth

How can I care for myself at home to stay in remission longer?

Besides medical treatment, self-care can truly reduce flare-ups:

Moisturize regularly, especially after bathing, to reduce cracking and peeling of the skin.
Avoid scratching or picking at scales, because skin injury triggers new rash at that spot.
Manage stress with rest, exercise and relaxing activities.
Quit smoking and cut down on alcohol.
Get moderate, gentle sunlight, which may help some people, but beware of sunburn, which can also trigger the disease.
Apply medicine as your doctor prescribes, continuously, even when the rash looks better, and attend follow-up appointments.

Frequently asked questions about psoriasis

Can psoriasis be cured?

There is currently no cure, but the disease can be controlled until the rash is barely visible with appropriate, continuous treatment. The goal is to keep the disease controlled so you can live normally.

Is psoriasis contagious by touch?

No. It is a disease of the person's own immune system. Touching or sharing belongings does not give the disease to others.

How is psoriasis different from seborrheic dermatitis?

Psoriasis usually forms thick, clearly red patches with sharp edges and silvery-white scales, while seborrheic dermatitis has greasy yellow scales with unclear edges. The two can occur together, and an examination by a dermatologist is the most accurate way to tell them apart.

Is it true that people with psoriasis must not eat eggs?

There is no evidence that people with typical psoriasis need to avoid eggs. It is more helpful to control weight, cut down alcohol and quit smoking.

Can nail psoriasis be treated?

Yes, but it usually takes longer than skin rash because nails grow slowly. The doctor may use topical medicine, injections into the affected area, or whole-body treatment in severe cases.

Does stress really trigger psoriasis flare-ups?

Yes. Stress is one of the most common triggers, so stress management is part of caring for the disease.

When should I see a dermatologist?

If you have a chronic red, scaly rash that does not clear with general care, a rash that comes and goes on the elbows, knees or scalp, or abnormal nails together with joint pain, seeing a dermatologist for a clear diagnosis early on helps you get the right treatment and lowers the chance that the disease progresses or becomes harder to control later.

At Siam Dermatology, our team of dermatologists places importance on a thorough differential diagnosis before starting treatment, because correct treatment starts with a correct diagnosis. If you have questions, you can consult us through the clinic's LINE OA at @siamderm.

Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed October 6, 2026