Ketoconazole, the active ingredient in Nizoral, works very well against the yeast Malassezia which causes the condition. It also soothes itching (pruritus), so it offers fast symptom relief even before any visible healing takes place.
In a clinical study, when a 2% ketoconazole cream was applied from the neck to the knees, it successfully cleared the infection in 98% of the 51 participants with tinea (pityriasis) versicolor. In comparison, only 28% of the 50 patients who received a placebo saw their infection clear. During follow-up, 80% of the people treated with ketoconazole 2% cream remained infection-free after one year, and 33% were still clear after two years.
The ketoconazole 2% shampoo was also shown to be effective in a study of 322 tinea versicolor patients. The results showed that 78% of those treated with ketoconazole shampoo for one day and 84% of those treated for three days were cured (compared to only 11% of those who received the placebo shampoo).
In a smaller study, 20 people with tinea versicolor were treated with 2% ketoconazole shampoo once a week for three weeks. After one month, 95% of the participants were cured, with only one person still experiencing mild symptoms.