How common is seborrheic dermatitis?

What do the numbers mean?

Prevalence means the proportion of people who have a condition, because statistics rarely lets a simple question keep its simple name. These global estimates cover cases diagnosed by clinicians, rather than people identifying their own rash.1

There is no single percentage that fits every country or setting. The uncertainty range around the global estimate is 3.58% to 5.17%, and rates differ substantially between populations. Country estimates include 8.82% in South Africa and 2.62% in India. General population surveys and clinics also capture different groups of people, so a high clinic percentage is not the same as the chance that any person has seborrheic dermatitis.1

Why do some figures say half of adults?

Dandruff and seborrheic dermatitis sit on the same spectrum, but counting them together gives a much larger number. Dandruff affects approximately half of adults worldwide. It mainly involves scalp flakes without visible inflammation. Seborrheic dermatitis includes inflammation and can affect the face, behind the ears and the upper chest as well as the scalp. Older adult estimates of 1% to 3% refer to seborrheic dermatitis, not everyone with dandruff.2

Who gets it most often?

Seborrheic dermatitis has peaks in the first three months of life, around puberty and in adulthood, particularly between ages 40 and 60. Men are affected somewhat more often than women. Dandruff has a different age pattern: it starts around puberty, peaks near age 20 and becomes less common after 50.2

Seborrheic dermatitis is also more common in people with weakened immune systems, including people with HIV and organ transplant recipients. It is associated with certain neurological conditions, including Parkinson's disease. These are group associations, not a way to diagnose another illness from scalp flakes.2

How common is cradle cap?

Cradle cap is seborrheic dermatitis on a baby's scalp. Estimates in infants up to three months old have reached 42%. That figure and the newborn estimate above cover different age groups and settings, so they are not interchangeable.23

Cradle cap is not caused by poor hygiene, is not an allergy and is not contagious. It often lasts a few months, although some children have it until age 2 or 3. Most cases can be managed at home with daily mild shampoo and gentle loosening of scales using fingers or a soft brush. Rinse the shampoo out fully. Once the scales disappear, shampooing can drop to twice weekly.34

What if you think you have it?

Seborrheic dermatitis is one type of eczema, not another name for every form of eczema. Symptoms can resemble other conditions, and a clinician can examine the skin to identify the cause. Common symptoms include itchy, scaly patches, often with greasy white or yellow scales.25

Dandruff shampoo often helps control scalp flakes, so the bottle's unusually literal job title is useful for once. If it does not help, contact a healthcare professional. Ketoconazole is an antifungal medicine available as a shampoo or cream for dandruff and seborrheic dermatitis; irritated skin is its most common side effect.46

For a baby, contact their clinician if home care does not help, symptoms worsen or persistent scratching causes discomfort. Get medical advice for fluid or pus, marked redness, pain or fever.3