A lot of black dots on the back of your arms may be related to diseases such as blackhead acne and pigmented moles. 1. Blackheads, also known as open pimples, are a common type of acne rash and a relatively early form of acne. The causes are mainly related to sex hormone secretion level, sebaceous gland secretion abnormality, Propionibacterium acnes infection and other factors. The main treatment is to give some anti-inflammatory and keratolytic drugs, such as adapalene gel. 2. Pigmented nevus is a kind of benign tumor located on the surface of the body, and its cause is related to factors such as heredity, ultraviolet radiation, trauma and drugs. The treatment is mainly laser therapy and cryotherapy, and it needs to be excised in time when the volume and shape change abnormally. Due to the complexity of the cause of the disease, a doctor’s consultation is required for specific cases. The use of drugs and treatment under the guidance of the doctor.