Skin petechiae are hemorrhagic patchy lesions on skin and mucous membranes with the same nature as bleeding spots, which mostly suggest hematological diseases or diseases causing bleeding and coagulation abnormalities. Clinically, it should be differentially diagnosed with the following symptoms: 1. Whole body skin congestion: Whole body skin congestion refers to the dilatation of whole body skin capillaries, and the dilated blood vessels are mostly small veins or small arteries, and red filiform, reticular or stellate damage appears on the skin. It makes the whole body skin congested, red and swollen. 2.Pigmented spots: mixed nevus in which nevus cells and nevus cells nest in the deep epidermis and also in the dermis is called mixed nevus. Commonly, the central nevus is protruding from the skin surface, with long hair, and the surrounding area is diffusely distributed, with different color and unclear boundary, which is the component of junctional nevus, and the junctional nevus changes to intra-dermal nevus since early childhood, so the mixed nevus is rarely seen in older people. Mixed nevus and junctional nevus both have the possibility of malignant transformation. 3. Discoid erythema: Discoid lupus erythematosus (DLE) is a chronic recurrent disease, mainly invading the skin, characterized by well-defined red plaques (erythema), hair follicle embolism, scaling, capillary dilation and skin atrophy. The etiology is unclear. It is more common in women, with the highest incidence around 30 years of age. The disease can be divided into two types: (1) limited skin lesions limited to the skin above the neck; (2) disseminated lesions involving a wide area of the skin. Some people believe that the disseminated type is easily transformed into SLE. 4. Facial pteroidal erythema: Facial pteroidal erythema is a facial symptom of SLE. Lupus erythematosus is an autoimmune disease with slow onset, insidious occurrence, diverse clinical manifestations and many changes an autoimmune disease involving many systems and organs, producing a variety of autoantibodies due to cellular and humoral immune dysfunction. It can involve skin, plasma membrane, joints, kidney and central nervous system, etc. It is characterized by autoimmunity, and there are many autoantibodies in the patient’s body, which not only affects humoral immunity, but also affects cellular immunity, and there are changes in complement system. 5.Coffee spots: Coffee spots, also known as coffee milk spots, are light brown patches that can be found at birth, with color ranging from light brown to dark brown, but the color of each patch is the same and very uniform, and the shade is not affected by sunlight, with size ranging from several millimeters to tens of centimeters, with clear borders and completely normal surface skin texture.