The appearance of red blood spots on the surface of the skin is considered to be related to allergic dermatitis, purpura, coagulation disorders and other factors. 1. Simple purpura: the onset of young women, often associated with the menstrual cycle, may be related to the effect of hormones on blood vessels and surrounding tissues. The main manifestation is purpura or ecchymosis of the skin of the lower limbs after minor trauma or spontaneously, the lesion is confined to the skin, often recurrent, but without sequelae. 2. Anaphylactic purpura: It is a more common capillary allergic reaction hemorrhagic disease. Petechiae under the skin and mucous membranes are common clinical symptoms, which can involve the skin, gastrointestinal tract, kidneys, joints, and even the heart, brain and other organs, with swelling and pain, abdominal pain, blood in stool, hematuria and proteinuria. 3. Coagulation dysfunction: patients may have red blood spots on the surface of the skin because of coagulation dysfunction, which further causes a decrease in the number or activity of coagulation factors, resulting in bleeding in subcutaneous tissues, muscles, and joints, and the formation of subcutaneous blood stasis. The appearance of red blood spots on the skin surface may also have other causes, and it is necessary to cooperate with the doctor to clarify the causes as soon as possible, and then do targeted treatment and therapy.