Small red dots on the thighs may be caused by mosquito bites, eczema, folliculitis, allergic purpura, pigmented purpuric dermatosis, psoriasis and other diseases. 1. Mosquito bites: mosquito bites will inject saliva into the local area, causing a delayed allergic reaction, resulting in the appearance of red dots on the skin, accompanied by itching. 2. Eczema: the onset of eczema is considered to be related to external material stimuli and mental factors, resulting in the appearance of localized pinheads, millet-sized papules, pimples, red dots. 3. Folliculitis: hair follicles are infected by bacteria causing inflammation, resulting in localized single, multiple red papules, which may also appear as red dots. 4. Anaphylactic purpura: Anaphylactic purpura, which may be caused by the dysfunction of the autoimmune system, leads to allergic inflammation of the skin, which sometimes affects many small blood vessels all over the body, resulting in skin rashes with an appearance similar to hemorrhagic dots. 5. Pigmented purpura dermatosis: the cause of the disease has not been fully clarified, and it is considered to be related to family genetics. Mainly manifested as thighs, calves in front, back of the hands and other parts of the appearance of pinpoint-sized bruises, bruises. 6. Psoriasis: the cause of the disease is not yet clear, the skin can appear red spots, which are covered with silvery-white silver flakes, and can also appear as a symptom of small red dots on the thighs. Red dots on the thighs, it is recommended to go to the dermatology department of the hospital in a timely manner to look for the cause of the red dots, and give treatment for the cause of the disease.