There are two main types of fungi. Moulds (e.g. dermatophytes) have long hyphae and grow from the tip. Yeasts (e.g. Malassezia and Candida) are single-celled organisms, shaped like rugby balls or footballs, that bud to produce new cells (Figure 20.2).

Pityriasis Versicolor (Figures 20.4 and 20.5)

Multiple patches coalesce over upper back, shoulders and chest in young adults, with light scaling, seen if gently scraped with spatula. ‘Pityriasis’ indicates fine scale, ‘versicolor’ means variable colour change: some areas become lighter, others darker. Caused by overgrowth of normal skin commensal lipophilic yeasts Malassezia globosa, Malassezia sympodialis and Malassezia furfur.

Treatment: ketoconazole shampoo applied three times or 2.5% selenium sulphide (Selsun® shampoo) applied on alternate nights for a week. Oral 200 mg/day itraconazole for 5 days if widespread.

Malassezia Folliculitis

Itchy papules and pustules on the back and upper body are seen in young adults. The differential diagnosis acne is not itchy.

Treatment: as for pityriasis versicolor.

Seborrhoeic Dermatitis, Dandruff

Superficial scaling in the sternal area, eyebrows (Figure 20.6), ears, nasolabial folds and diffusely throughout scalp is seen. Adult seborrhoeic dermatitis is caused by Malassezia species.

Treatment: as for pityriasis versicolor.

Dermatophyte Infections

Tinea Pedis (‘Athlete’s Foot’) (Figure 20.7)

The most common fungal infection, spread by walking in communal changing rooms. Macerated skin between the fourth and fifth toes is seen; it may involve other toe webs, the sole or dorsum of the foot. Vesicles may coalesce, forming bullae because of thick stratum corneum. Usually caused by Trichophyton rubrum.