What is seborrheic dermatitis?

You suspect you have seborrheic dermatitis or your doctor has diagnosed you with seborrheic dermatitis: what do you need to know about this skin and scalp condition? 
It is a common condition, generally benign, although it can severely affect quality of life. It is currently ranked as the third most likely skin condition to disrupt daily life, just after atopic dermatitis and contact dermatitis (1).
How does it manifest? What areas of the body can be affected? Find out everything you need to know to identify and understand seborrheic dermatitis.

Areas affected by seborrheic dermatitis

Lesions develop in so-called “ oily ” areas of the skin, where sebum secretion is highest. The areas most affected are the scalp, the crease between the nose and cheeks (also known as the nasolabial fold), the eyebrows and the space between them, and sometimes the chest. In the same person, seborrheic dermatitis can affect several of these areas at the same time.

What more do we need to know about the prevalence of seborrheic dermatitis? 

• Men (1.9%) are slightly more affected than women (1.6%) ⁽²⁾
• Seborrheic dermatitis mainly affects people aged between 16 and 39 ⁽²⁾

Seborrheic dermatitis of the torso

Seborrheic dermatitis of the torso is much less common than seborrheic dermatitis of the face (which affects more than 65% of cases ⁽³⁾) or scalp seborrheic dermatitis (which affects more than 80% of cases ⁽³⁾). 
It affects around 25% to 30% of people with this condition ⁽³⁾. 
This form of seborrheic dermatitis manifests itself as red, scaly patches in the middle of the chest, especially between the breasts and more rarely on the back.

Seborrheic dermatitis on the body

Seborrheic dermatitis can sometimes appear on the body, particularly in the genital area and groin folds, but this is very rare. It mainly affects areas rich in sebaceous glands, which explains why it rarely affects parts of the body where there are fewer of these glands. 
It affects around 25% to 30% of people with this condition ⁽³⁾.
This form of seborrheic dermatitis manifests itself as red, scaly patches in the middle of the chest, especially between the breasts and more rarely on the back.

Differential diagnosis of seborrheic dermatitis

To diagnose seborrheic dermatitis correctly, what do you need to know?

In general, the visible signs of this disease are enough for the doctor to make the correct diagnosis. However, in some cases, the lesions can resemble those of psoriasis, eczema or rosacea, which can make diagnosis more complicated.

Here's how to tell the difference between these three conditions:

• Eczema manifests as red patches with small blisters filled with clear fluid, accompanied by very intense itching and dry skin. The difference between eczema and seborrheic dermatitis is not always obvious, but eczema lesions often extend beyond the “ oily ” areas of the skin and are generally found in the creases of elbows, knees, etc.
• Psoriasis is characterised by thick scaly red patches. Psoriasis or seborrheic dermatitis? It's not always easy to tell them apart, especially on the face. Psoriasis patches are drier, well-defined and often found on areas of friction such as the elbows, knees or lower back. When psoriasis affects the face, it is sometimes called sebopsoriasis. 
• Rosacea that is vascular in origin is characterised by persistent redness of the nose, cheeks and sometimes the chin and forehead, often with a tingling sensation. Rosacea lesions may resemble those of seborrheic dermatitis, but rosacea does not cause surface scaling, which helps to differentiate them. 

Infant seborrheic dermatitis

When seborrheic dermatitis affects infants, it is better known as cradle cap. It generally appears in the first three months of life and affects around 4 out of 10 babies ⁽⁴⁾. 

The main cause is the same as in adults: a yeast of the genus Malassezia which proliferates excessively on the skin of some infants. Fortunately, these cradle caps are painless and itch-free for the baby and often disappear spontaneously between 4 and 6 months of age⁽⁴⁾.

What do you need to know about treating this type of seborrheic dermatitis? In infants, it is generally not necessary to use medication, except in very severe cases. The best approach is to maintain regular hygiene by using dermo-cosmetic products specially formulated to eliminate cradle cap.