Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain dark discolouration of face and neck can occur due to a number of causes out of which common ones are sun exposure, side effects of any skin cosmetics, allergic reactions while can also occur due to causes like Acanthosis Nigricans,intake of oral contraceptive pills, thyroid disorders, stress,freckles, hemocromatosis [increased iron content in body] etc.. Consult a Dermatologist and get evaluated.. A thorough clinical examination and investigations like complete blood picture, hormonal assy etc can help in diagnosis and treating the underlying cause can resolve the symptoms.. Hyperpigmentation caused due to excessive melanin formation can be treated with depigmentation creams like those containing Kojic acid, glycolic acid, Vitamin E.. Grapessed extreact, licorice etc can help.. Using depigmenting facewash like those containing Salicylic acid and glycolic acid can help.. Treatments like Microdermabrasion and chemical peeling will help.. But if it is due to any underlying disorder treatment of the same has to be preceeded following the depigmentation treatment.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.