In my assessment, you are referring to the condition called as tinea versicolor (Pityriasis versicolor), caused by Malassezia furfur. It produces asymptomatic hypo- or hyperpigmented spots over the upper trunk. Diagnosis needs to be confirmed by KOH examination of the skin scrapings of the affected areas. Treatment can be topical or systemic depending upon the extent of involvement. The treatment is sought mainly for cosmetic reasons.
Topical therapy:
1. 20% sodium hyposulfite lotion or sodium thiosulphate lotion topically twice daily over affected areas for 3 to 4 weeks.
2. 2.5% selenium sulphide as shampoo for 5 to 10 minute application daily for 3 to 4 weeks.
3. Imidazole derivatives topically are also effective.
Systemic therapy:
Griseofulvin is not effective. In resistant and extensive cases, ketoconazole (200 mg daily orally for 5 to 10 days), fluconazole (single oral dose of 400 mg) and itraconazole (200 mg daily for 5 to 7 days) may be tried. Pigmentation persists for weeks or months after the disease is cured unless an effort is made to regain the lost tan.