A lot of pimple-like red dots on the thighs may be related to contact dermatitis, eczema, and purpura allergic. 1. Contact dermatitis refers to the skin of the lower extremities in contact with some kind of stimulating substances and the occurrence of allergic reactions, the clinical main manifestations of local skin pimples, erythema, and small blisters and so on, for example, contact with metal, contact with chemical substances, and so on. 2. Eczema is a chronic skin disease formed under the influence of a variety of internal and external factors, which can be manifested in the clinic as small pimples and maculopapular rashes with itching that slightly protrude from the skin surface. 3. Henochromatosis purpura is a vascular metamorphic reaction disease, which is mainly manifested in the clinic as small pinpoint hemorrhages under the mucous membrane of the skin, with no discoloration when pressed locally. Due to the complexity of the etiology, there are a lot of small red dots on the thighs like pimples may also have other causes, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, to give targeted treatment or treatment.