Overview
Dandruff, seborrheic dermatitis (seborrhea), and psoriasis are chronic, scaly dermatoses that involve the uppermost layer of skin (the epidermis).
Dandruff is a chronic, mildly inflammatory scalp disorder. In patients with dandruff, an accelerated epidermal cell turnover (twice that of normal scalp) and an irregular keratin breakup pattern result in the shedding of large, nonadherent white scales. Most cases of dandruff are amenable to self-treatment.
Seborrheic dermatitis is a subacute or chronic inflammatory disorder marked by accelerated epidermal proliferation in areas with dense distribution of sebaceous glands (e.g., scalp, face, and trunk). It appears as areas of red, itchy skin with prominent yellow or oily lesions. Most cases of seborrheic dermatitis are amenable to self-treatment.
Psoriasis is a chronic inflammatory disease marked by accelerated epidermal proliferation that leads to excessive scaling on raised plaques. Lesions often are localized but may become generalized over much of the body surface. Self-treatment of mild psoriasis is appropriate only after an initial diagnosis by a primary care provider or dermatologist.
Epidemiology
- Dandruff occurs in approximately 1%–3% of the population. There is no gender preference.
- Dandruff is uncommon in children. It generally appears at puberty, reaches a peak in early adulthood, levels off in middle age, and is less prominent after 75 years of age.
- Seborrheic dermatitis is common in infants (within the first 3 months of life) and affects 2%–5% of adults (typically around the fourth to the seventh decade of life).
- Men are affected more commonly than women.
- Psoriasis is estimated to afflict 1%–3% of Americans, with an equal distribution among men and women.
- Psoriasis is seen in all races and geographic regions, but the incidence is lower among people living in countries close to the equator and among blacks, Native Americans, and Asians.
Etiology
- The specific cause of accelerated cell growth seen in dandruff has been controversial. Debate continues as to whether dandruff is a result of accelerated cell turnover due to elevated levels of microorganisms, particularly the fungus Malassezia.
- Seborrheic dermatitis is caused by elevated levels of Malassezia. Emotional stress may serve as an aggravating factor.
- The cause of psoriasis is unknown. The onset of psoriasis can be triggered by a number of factors, including environmental factors, streptococcal and viral infections, medications, psychological stress, endocrine or hormonal changes, obesity, and use of alcohol or tobacco.
Signs and Symptoms
- See Table 1 for a summary of the distinguishing features of dandruff, seborrheic dermatitis, and psoriasis. Additional information is provided in the following sections.
TABLE 1. Distinguishing Features of Scaly Dermatoses
| Dandruff | Seborrheic Dermatitis | Psoriasis |
Location | Scalp | Adults and children: head and trunk; children only: back, intertriginous areas | Scalp, elbows, knees, trunk, lower extremities |
Exacerbating factors | Generally a stable condition, exacerbated by dry climate | Exacerbated by many external factors, notably stress | Exacerbated by irritation, stress, climate, medications, infection, endocrine factors |
Appearance | Thin, white, or grayish flakes; even distribution on scalp | Macules, patches, and thin plaques of discrete yellow, oily scales on red skin | Discrete symmetrical, red plaques with sharp border; silvery white scale; small bleeding points when scale is removed; difficult to distinguish from seborrhea in early stages or in intertriginous zones |
Inflammation | Absent | Present | Present |
Epidermal hyperplasia | Absent | Present | Present |
Epidermal kinetics | Turnover rate 2 times faster than normal | Turnover rate about 3 times faster than normal | Turnover rate about 5–6 times faster than normal |
Dandruff
- Dandruff is characterized by the sloughing of large white or gray scales. It is diffuse rather than patchy and is minimally inflammatory. The crown of the head often is a prime location for formation of dandruff flakes.
- Pruritus is common although not universal in all patients.
Seborrheic Dermatitis
- Seborrheic dermatitis typically presents as dull, yellowish, oily, scaly areas on erythematous skin. The scaly areas are fairly well demarcated.
- Pruritus is common.
- The infantile form of seborrheic dermatitis usually affects the scalp (cradle cap), retroauricular creases, lateral neck, and intertriginous folds. It presents as greasy scales and crusts on a bright erythematous base.
- Cradle cap usually clears without treatment by 8–12 months of age as hormones passed from the mother to the child before birth gradually disappear.
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