A lot of tiny red dots on the arms and body may be caused by diseases such as eczema, purpura, cherry angiomas and periosteal keratosis. 1. Eczema: In people with sensitive bodies, skin contact, consumption, and inhalation of allergens lead to skin metamorphosis and eczema. Pimples and erythema may appear on the skin, which may be accompanied by obvious itching sensation. 2. Purpura: Purpura is commonly seen in allergic purpura and thrombocytopenic purpura, clinically manifested as petechiae and ecchymoses of different sizes, which may be accompanied by abdominal pain, arthralgia, fever and other manifestations. 3. Cherry angioma: red rice-sized papules on the trunk of middle-aged and elderly people are considered to be related to cherry angioma, which is also called senile angioma. 4. Keratosis pilaris: the appearance of small, reddish, keratinized papules on the arms or body may also be considered to be related to genetically caused keratosis pilaris. There may be other reasons for the appearance of many small red dots on the arms and body, it is recommended to go to the hospital in a timely manner, improve the relevant examination, a clear diagnosis, symptomatic treatment.