Pityriasis (tinea) versicolor and seborrheic dermatitis are two very common skin diseases. Pityriasis versicolor is a chronic superficial fungal disease usually located on the upper trunk, neck, or upper arms. In pityriasis versicolor, the lipophilic yeast Malassezia (also know as Pityrosporum ovale or P. orbiculare) changes from the blastospore form to the mycelial form under the influence of predisposing factors. The most important exogenous factors are high temperatures and a high relative humidity which probably explain why pityriasis versicolor is more common in the tropics. The most important endogenous factors are greasy skin, hyperhidrosis, hereditary factors, corticosteroid treatment and immunodeficiency. There are many ways of treating pityriasis versicolor topically. Options include propylene glycol, ketoconazole shampoo, zinc pyrithione shampoo, ciclopiroxamine, selenium sulfide, and topical antifungals. In difficult cases, short term treatment with fluconazole or itraconazole is effective and well tolerated. To avoid recurrence a prophylactic treatment regimen is mandatory. Seborrheic dermatitis is characterized by red scaly lesions predominantly located on the scalp, face and upper trunk. There are now many studies indicating that Malassezia plays an important role in this condition. Even a normal number of Malassezia will start an inflammatory reaction. Mild corticosteroids are effective in the treatment of seborrheic dermatitis. However, the disease recurs quickly, often within just a few days. Antifungal therapy is effective in the treatment of seborrheic dermatitis and, because it reduces the number of Malassezia, the time to recurrence is increased compared with treatment with corticosteroids. Antifungal therapy should be the primary treatment of this disease.