It is a common observation that various types of local trauma to the skin, such as burns, x-rays, inflammatory skin diseases, or pruritic conditions, initially cause a hyperpigmentation but if severe or of long duration may cause depigmentation. Usually, when the irritating factor is removed, the skin again repigments.
A large number of the vitiligo patients seen in the Dermatology Clinic of the Christian Medical College Hospital, Vellore, South India, gave a history of some type of skin involvement or irritation in the specific area which later depigmented. In these cases depigmented macules also appeared in other nonaffected parts of the body. Ormsby and Montgomery1 state that vitiligo "occurs in association with or follows certain cutaneous diseases such as lichen planus, psoriasis, alopecia areata and local pruritis. . . . It occasionally follows local irritation, trauma through scratching and irritant applications such as formalin." G. Asboe-Hansen
LEVAI M. The Relationship of Pruritus and Local Skin Conditions to the Development of Vitiligo. AMA Arch Derm. 1958;78(3):372–377. doi:10.1001/archderm.1958.01560090088018