The underlying mechanism which causes Vitiligo is loss of melanin. This occurs due to destruction of existing melanocytes and defective formation of new melanocytes. However, the precise reason why the melanin is lost and what causes the destruction of these pigment-forming cells is not completely understood.

A combination of auto-immune, genetic & environmental factors has been seen in most cases. Recent studies have demonstrated that Vitiligo may also be caused by stress which affects the immune system, leading the body to react and mistakenly destroy the melanocytes by releasing antibodies against them.

Heredity has been strongly proposed as a cause since many cases with Vitiligo do report incidence of this condition (or other auto-immune disorders) in their family. Research has also shown the NALP1 gene to be the trigger in predisposing people to Vitiligo.

Additionally, Vitiligo is said to be associated with (and affecting people with) certain auto-immune and inflammatory diseases such as:

Hypothyroidism - Under -functioning of thyroid gland

Hyperthyroidism - Over -functioning of thyroid gland

Diabetes mellitus

Addison's disease

Alopecia areata

Psoriasis

Pernicious anemia

Possible things that can trigger Vitiligo in an individual who is genetically prone include:

Skin trauma

Sun burn

Emotional stress

Skin rash

Exposure to de-pigmenting chemicals - the disease can later spread beyond areas of contact via immune-mediated mechanism. Phenolic/catecholic derivatives are the prime chemicals causing this.

All said and done, the exact reason why Vitiligo affects some people and not others, and that too with such unpredictability, still remains unexplored!