The skin of the underarms and neck can sometimes darken or become discoloured. Underarm skin that's darker than the rest of the skin can be a distressing problem for most of us. It keeps us from wearing sleeveless clothes.
What are the causes of dark underarms and neck?
Chemical irritants in deodorants and antiperspirants
The accumulation of dead skin cells
Friction caused by tight clothes
Hyperpigmentation such as an increase in melanin
Acanthosisnigricans , a skin pigmentation disorder that's associated with diabetes, obesity , and abnormal hormone levels.