What Causes Birthmarks? A Dermatologist Explains Red, Dark and Nevus of Ota Birthmarks, Which Fade on Their Own, Which Are Dangerous, and Which Laser Matches Each Type
Birthmarks are skin lesions present from birth or appearing in the first year of life, caused by abnormalities of the blood vessels or pigment cells under the skin. Most birthmarks are harmless and some fade on their own, but a few can signal an underlying condition or need treatment from childhood for the best result. In this article, a dermatologist explains how to tell each type apart, which ones fade on their own, which need prompt medical attention, and why choosing the 'right laser for the type' matters more than most people think.
Many families mistakenly believe that 'a birthmark is just a birthmark' and assume it will fade as the child grows, or that any laser clinic will do. In fact, each type of birthmark has a completely different origin, behavior and treatment. Identifying the type correctly is the first step, before deciding whether to observe, treat or order further tests.
What Causes Birthmarks? Two Main Groups
The standard medical classification divides birthmarks by their cell of origin into two main groups, which is the key to both diagnosis and laser selection:
Vascular birthmarks — caused by abnormal or excessive small blood vessels, appearing red, pink or purple. The pigment the laser must target is hemoglobin in red blood cells.
Pigmented birthmarks — caused by pigment-producing cells (melanocytes) that are misplaced or excessive, appearing brown, black or blue-gray. The pigment the laser must target is melanin.
A simple rule to remember: a laser designed to target hemoglobin does not work on pigmented birthmarks, and a laser that targets melanin does not work on vascular birthmarks either. This is why the type must always be identified before any laser treatment.
Red Birthmarks (Vascular Group): What Types Are There?
There are three common types of red birthmark, and they behave very differently:
Salmon patch (Nevus simplex) — a faint pink patch that is the most common birthmark in babies, usually on the back of the neck (nicknamed the 'stork bite') or the middle of the forehead and eyelids (nicknamed the 'angel kiss'). It becomes more visible when the baby cries. Those on the face mostly fade on their own within 1–2 years. Those on the back of the neck may last a long time or be permanent, but they are not dangerous.
Infantile hemangioma — found in about 3–10% of babies. The key point is that it is often not visible at birth but appears in the first few weeks, then grows quickly over the first several months (proliferative phase) before gradually shrinking on its own over several years. However, shrinking on its own does not always mean the skin returns to smooth: about 15–40% leave behind loose skin, small visible blood vessels or scarring.
Port-wine stain (Capillary malformation) — a dark red to purple patch that is present from birth and does not fade on its own. On the contrary, it usually becomes darker and thicker with age and can develop raised bumps in adulthood. This type responds well to lasers that target blood vessels and should be treated early.
Dark and Brown Birthmarks (Pigmented Group): What Types Are There?
There are four common pigmented birthmarks that you should be able to tell apart:
Mongolian spot (Dermal melanocytosis) — a blue-gray or dark greenish patch on the tailbone and lower back, very common in Asian babies. It is harmless and usually fades on its own during childhood. Be aware that it looks like a bruise, so it should not be mistaken for an injury.
Café-au-lait macule — an evenly light brown patch with smooth edges, which can be present from birth. One or two spots usually mean nothing, but many spots, or large ones, can be a clue to a genetic condition (see the warning signs section).
Congenital melanocytic nevus — a dark brown to black patch or lump present from birth, sometimes with hair. What matters is its size, because the larger the birthmark, the higher the risk of developing melanoma skin cancer, so long-term follow-up is needed.
Nevus of Ota — a blue-gray or purple-brown patch on one side of the face, usually around the eye, cheek and temple, caused by pigment cells deep in the dermis. It does not fade on its own and usually darkens with age. Some people also have dark pigment in the white of the eye. This type responds well to lasers that target pigment.
Which Birthmarks Fade on Their Own and Which Are Permanent?
To make this clearer, here is how each type behaves:
Usually fade or lighten on their own: salmon patches on the face, Mongolian spots, and infantile hemangioma (shrinks on its own, but some leave marks behind)
Permanent and usually darken if untreated: port-wine stain, nevus of Ota, congenital melanocytic nevus, café-au-lait macule
The safe approach is not to assume every birthmark will fade on its own, because waiting on a birthmark that will never fade only lets it darken and makes it harder to treat.
Warning Signs: Which Birthmarks Need Prompt Medical Attention
Most birthmarks are harmless, but some features can be clues to conditions that need a doctor's evaluation. See a dermatologist or pediatrician if you notice any of the following:
A port-wine stain on the forehead and upper eyelid (upper branch of the facial nerve) — may be associated with Sturge-Weber syndrome, which carries a risk of raised eye pressure (glaucoma) and seizures, and requires an eye examination and neurological assessment.
A large hemangioma covering a wide area of the face (segmental) — may be associated with PHACE syndrome and needs further investigation.
A hemangioma around the eyes, nose or mouth, or spread in a 'beard' pattern — risks interfering with vision, breathing or feeding, and should be assessed early.
A very large congenital melanocytic nevus — carries a higher risk of melanoma, and some cases are linked to pigment cell involvement of the nervous system, so close follow-up is needed.
Six or more café-au-lait macules that meet the size criteria (more than 0.5 cm in children / more than 1.5 cm in adults) — this is one of the criteria for suspecting Neurofibromatosis type 1.
A birthmark that changes unusually fast — growing quickly, changing color, having irregular borders, ulcerating, bleeding, or becoming itchy or painful should be examined with a dermatoscope (dermoscope) to distinguish it from skin cancer.
Why 'Wait Until They Grow Up' May Mean Missing the Golden Window
The blanket advice to 'deal with it when they're older' does not apply to every birthmark, and in some cases waiting costs the best chance of treatment:
Problematic infantile hemangioma responds best to oral propranolol during the rapid growth phase, which is the first few months of life. This medicine is the standard treatment, supported by large studies. Waiting until this phase has passed leads to poorer results.
Port-wine stains respond better to vascular lasers when treatment starts while the skin is still thin and the birthmark is still light. Leaving it until later lets it become thicker and darker, requiring more sessions and giving poorer results.
On the other hand, harmless birthmarks that usually fade on their own, such as Mongolian spots or salmon patches on the face, do not need any urgent action; just watch for changes. The key is to diagnose the correct type first and then decide whether to observe or treat.
Which Laser Matches Which Type: Do Not Use the Wrong Group
A common misconception from advertising is that 'Pico laser removes every birthmark', which is not true mechanically, because each laser is designed to target a different thing:
Vascular birthmarks (port-wine stain, hemangioma) — need a laser that targets hemoglobin, such as the Pulsed Dye Laser (PDL 595 nm) for superficial lesions, or a longer-wavelength laser (such as 1064 nm) for deeper lesions.
Deep pigmented birthmarks (nevus of Ota) — need a laser that targets melanin, such as a Q-switched or Picosecond laser, whose energy shatters the pigment in the dermis.
If a pigment laser is used on a vascular birthmark, or a vascular laser on a pigmented birthmark, the result is wasted money, wasted time and no visible improvement, and sometimes an unnecessary risk of burns or discoloration. The choice of laser must therefore come from a correct diagnosis of the birthmark type, not from the name of a machine advertised as the best.
How Are Birthmarks Diagnosed?
A dermatologist diagnoses a birthmark from several elements together:
History of when it appeared — present from birth (such as a port-wine stain or congenital melanocytic nevus) or appearing later (such as a hemangioma) is an important clue.
Clinical appearance and location — color, borders, thickness and location (especially vascular birthmarks on the face, which need additional risk assessment).
Dermatoscope (dermoscope) — helps distinguish harmless pigmented birthmarks from lesions suspected to be skin cancer.
Additional tests in selected cases — some cases need an eye examination, brain imaging or referral to other specialists when a birthmark-related syndrome is suspected.
Evaluation by a specialist is therefore worth more than simply 'removing it for looks', because it screens for hidden conditions and plans treatment that matches the type from the start.
Frequently Asked Questions (FAQ)
Can birthmarks fade on their own?
It depends on the type. Salmon patches on the face and Mongolian spots usually fade on their own in childhood, and infantile hemangiomas often shrink on their own, but port-wine stains, nevus of Ota, congenital melanocytic nevi and café-au-lait macules are usually permanent and may darken if untreated.
Are red birthmarks in babies dangerous?
Most are not dangerous, but location and size matter. A port-wine stain on the forehead and upper eyelid, a large hemangioma on the face, or one around the eyes, nose, mouth or airway should be evaluated by a doctor because it may be associated with conditions that need additional care.
Can lasers remove birthmarks, and which is best?
Yes, but the laser must match the type. Vascular birthmarks use lasers that target blood vessels (such as the Pulsed Dye Laser), while deep pigmented birthmarks such as nevus of Ota use lasers that target pigment (Q-switched or Picosecond). No single laser removes every birthmark.
When should birthmark treatment start, and do I have to wait until the child grows?
For many types, the earlier treatment starts, the better the result, especially port-wine stains, which should be lasered while the skin is still thin, and problematic hemangiomas, which respond well to medicine during the rapid growth phase. Waiting may mean missing the window when treatment works best.
Can a congenital melanocytic nevus become cancer?
There is a risk, especially with very large congenital melanocytic nevi. The risk is related to the size of the birthmark, so it should be monitored and checked with a dermatoscope regularly. If it changes quickly, see a doctor.
Is having several café-au-lait macules abnormal?
Having six or more that meet the size criteria (more than 0.5 cm in children, more than 1.5 cm in adults) is one of the criteria for suspecting Neurofibromatosis type 1 (NF1). You should see a doctor for further evaluation.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed August 20, 2026
Evidence-Based References
Léauté-Labrèze C, et al. A randomized, controlled trial of oral propranolol in infantile hemangioma. N Engl J Med. 2015.
American Academy of Pediatrics — Clinical Practice Guideline for the Management of Infantile Hemangiomas.
DermNet — Vascular birthmarks; Congenital melanocytic naevus; Naevus of Ota.
American Academy of Dermatology — Birthmarks.
Note: This article provides general information for basic understanding and is not a substitute for an in-person diagnosis. Appropriate treatment requires an individual assessment by a doctor.
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