Dense black spots on the arms are mostly due to keratosis pilaris, which can be relieved by medication and other means. Keratosis pilaris is a chronic follicular keratinizing skin disease, which has a certain genetic predisposition, and vitamin A deficiency is also related to keratosis pilaris. It usually occurs on the outer sides of the upper arms and the anterior sides of the thighs as small, corn-like papules with light brown keratin plugs at the tips, which appear to be densely packed black dots. Usually there are no obvious discomfort symptoms of perifollicular keratosis and it can be left untreated. If you want to improve the skin condition, you can relieve the skin by using topical vitamin A acid ointment, urea cream, salicylic acid ointment and so on. Severe cases can be treated with oral vitamin A, vitamin E or retinoids. The appearance of dense black spots on the arm, you should promptly go to the hospital, clear cause, under the guidance of the doctor symptomatic treatment, the specific use of drugs need to follow the doctor’s instructions.