The skin is located on the surface of the human body and is a mirror reflecting the health of the whole body. An individual in good health and good nutritional status will have a rosy complexion and lustrous, elastic skin. When the health condition is not good, the face is often emaciated. Those who are malnourished have dry skin and lose elasticity. Changes in the skin can be precursors or indications of systemic diseases, such as a young woman with chronic fever and arthralgia, when butterfly-shaped erythema appears on the face, it indicates a possible patient with systemic lupus erythematosus, such as an elderly person with itchy skin and prone to skin infections such as folliculitis, boils or Candida infections, should be checked for urine sugar and blood glucose, except for the presence of diabetes. So, what are the conditions that require a hospital visit and what are the common skin diseases included? What kind of signs and symptoms will occur when skin diseases occur? 1.What are the common skin diseases? There are more than a thousand kinds of skin diseases, the most common ones are 6 types: (1) Infectious skin diseases: ① Viral infectious skin diseases are divided into herpes virus and papilloma virus infections. The former has herpes simplex, genital herpes, chicken pox and herpes zoster, the latter has common warts, plantar warts, flat warts and condyloma acuminata; ② bacterial infectious skin disease is divided into coccus infectious skin disease, impetigo, folliculitis, boils, dengue and gonorrhea. Mycobacterial infectious skin diseases, there are leprosy and tuberculosis. Fungal infectious dermatoses include ringworm, ringworm, ringworm and nail fungus. (2) Allergic dermatoses: contact allergic dermatitis, eczema, atopic dermatitis, urticaria and drug rash. (3) Erythematous scaling dermatoses: pityriasis rosea, psoriasis (psoriasis), pityriasis simplex, lichen planus, and seborrheic dermatitis. (4) Vasculitis and lipofuscinosis: allergic cutaneous vasculitis, allergic purpura, Sweet’s disease, leukodystrophy, pigmented purpuric dermatosis, erythema nodosum, Weber-Christan lipofuscinosis, nodular wandering lipofuscinosis, Rosman-Maki lipofuscinosis. (5) Skin appendage diseases: acne, rosacea. (6) Pigmented dermatoses: divided into pigment-increasing dermatoses and pigment-reducing dermatoses. The former are freckles, chloasma and nevus of Ota, while the latter are vitiligo, halo nevus, anemic nevus, depigmented nevus and senile leukoplakia, etc. 2.What are the common symptoms of skin diseases? Symptoms of skin diseases, also known as clinical manifestations of skin diseases, are an important basis for recognizing and diagnosing skin diseases, which are generally divided into conscious symptoms and objective symptoms. Conscious symptoms are the symptoms felt subjectively, which are the way of expression of the nature of dermatological diseases. The main sensations are itching, pain and numbness, followed by foreign body sensation and abnormal response to temperature. Because of individual differences in people, the perception of sensations such as itch and pain varies. Itching is the most common sensory symptom in dermatology, and it is mainly a manifestation of allergic skin diseases and some infectious skin diseases, reflecting the nature of the disease as a result of allergy. Common diseases include various eczema and dermatitis, urticaria and drug rash. In addition some infectious skin diseases such as impetigo and tinea pedis and some malignant tumors such as mycosis fungoides. Pain is the second most common sensory symptom in dermatology, which reflects the nature of the disease as an infectious skin disease, such as: folliculitis, boils, dermatitis, cellulitis, herpes simplex, herpes zoster, and genital herpes. There are also vasculitis, lipofuscinosis, dermatofibromas and smooth muscle tumors. Numbness and diminished or absent sensation to heat and cold are the cutaneous manifestations of leprosy. Objective symptoms are the abnormal cutaneous manifestations of the skin disease, also called lesions or rashes. These lesions are divided into primary rashes including macules (plaques), papules, bumps, nodules, blisters, pustules, cysts and secondary rashes including scales, maceration, erosions, ulcers, fissures, epidermal scratches, scarring, mossy changes, atrophy, etc. Clinicians refer to these symptoms, which can be observed or examined, as signs. Therefore, when your skin has the above mentioned abnormalities including sensory abnormalities such as itching, pain, etc. or a rash, you should try to go to a regular hospital instead of self-treating and delaying the treatment.