Check With Your Doctor.

Check with your doctor. Home remedies may not help with dark underarms if you're suffering from a condition known as acanthosis nigricans, a skin disorder that results in velvety, light-brown-to-black markings in areas that include the armpits. This condition can occur as a result of obesity or an endocrine (glandular) disorder. It is frequently found in people with diabetes or a tendency towards diabetes and is most common among people of African descent.

Other possible causes of acanthosis nigricans include Addison's disease, pituitary gland disorders, growth hormone therapy, hypothyroidism or the use of oral contraceptives