Skin cancer is superficial, unlike a type of cancer deep inside the body, which people do not care enough and often ignore, but in fact skin cancer is quite common. Because of the special location of skin cancer, it can be seen or touched by oneself. As long as one has some basic knowledge of common skin cancer and pay attention to it, it is not difficult to detect it at an early stage. The symptoms of various skin cancers are classified as follows: 1. Squamous cell carcinoma, called squamous carcinoma for short, is named after the malignant transformation of squamous epithelial cells of the skin and is one of the common typical skin cancers. Squamous cell carcinoma mostly occurs in areas with chronic inflammation, such as burn scars, chronic ulcers, lupus erythematosus, psoriasis, etc., but rarely occurs in normal skin and mucous membrane. The early manifestation of squamous carcinoma is small red hard nodules, the surface of which can be warty or papilloma-like; it can also manifest as ulcers with clear edges, uneven bottom, small granulomatous protrusions, and easy bleeding. At first, squamous carcinoma does not cause pain and is easy to be ignored. Later, the ulcer will enlarge and the edge will be turned out, or cauliflower-like new organisms will grow on the ulcer surface, and lymph node metastasis may have occurred at this time. The metastasis is especially early for squamous carcinoma that occurs in lip, tongue and external genital area. Once squamous carcinoma causes pain, most of them have already invaded deep tissues and metastasized, which will be very difficult to treat. Therefore, when abnormal changes occur in chronic inflammatory areas of skin and mucous membrane, timely diagnosis and treatment and pathological examination must be carried out. Basal cell carcinoma is named because the shape of cancer cells resembles basal cells of skin. In contrast to squamous carcinoma, basal cell carcinoma often occurs on normal looking skin. Its early symptoms are not obvious and its morphology is diverse, but it still has the following characteristics: it usually occurs in hairy areas, especially in exposed areas such as scalp, eye area, nose and nasolabial folds. Initially, they are small, round, pearl-like elevations above the skin surface, and later they form hard nodes or small ulcers, and the ulcers around the eyes and nose can quickly develop deeper, but lymph node metastasis is much less common than squamous carcinoma. In addition, there is a kind of pigmented basal cell carcinoma, which appears as melanosis at the hard nodes or ulcers, and is easily mistaken as a nevus and let down the vigilance. Although the malignancy of basal cell carcinoma is not high and metastasis is rare, it is easy to cause tissue destruction and early detection and treatment is recommended. 3.Carcinoma in situ, also known as Bowen’s disease, is named because the cancerous cells develop confinedly in the epidermis for a long time. Patients are mostly above 40 years old, more males than females, often occurring in the trunk and limbs, and are mostly solitary. In the early stage, it is an unnoticeable dark red papule with scales or crusts, and later it gradually expands into flakes or rings with thick crusts, which can be easily mistaken for psoriasis or eczema. If left untreated, it will evolve into squamous carcinoma over time. It is worth noting that according to statistics, more than half of the people suffering from this disease are complicated by internal tumors, which shows that early diagnosis and detailed whole body examination are very necessary. 4.Eczema-like tumor There are two types, one is called eczema-like carcinoma of breast, which mainly occurs in women above middle age. It starts as erythema of unilateral nipple and nipple areola with clear boundary, a small amount of ooze and crust, resembling eczema, with itching and burning pain, but treatment as eczema is ineffective. Over time, the area may gradually expand beyond the areola and a lump may be found in the breast. Unilateral onset and eczema-like manifestations are characteristic of this disease. It is now known to be associated with ductal carcinoma of the breast, so the earlier the diagnosis, the better. Another type of eczema-like carcinoma, called eczema-like carcinoma of the external breast, can occur in both men and women over 50 years of age. The most common sites are the female pubic area, scrotum, penis, perianal area, axilla, umbilicus and other areas with sweat gland distribution. It starts with erythema, oozing and itching, and is similar to eczema-like carcinoma of breast. Eczema-like carcinoma outside the breast can also be accompanied by carcinoma of the sweat gland and other internal organs, so comprehensive examination is needed to exclude them. 5.Malignant melanoma is the most malignant skin cancer, which can easily metastasize. It occurs mostly in middle-aged and elderly people, and trauma and sunlight are possible causes. It can occur on normal skin and mucous membrane as well as on junctional nevi. The most common types are superficial and nodular. Superficial nevi are usually found on the back of men and calves of women, and are curved or irregular dark brown or gray patches with nodules of different sizes, expanding up to 2.5 cm in diameter; nodular nevi are usually found on the head and face, palmoplantar, extremities, under the nails, etc., and can also occur on mucous membranes. The nodules are initially black and raised like “white blisters”, but later they rapidly increase in size, break down, and metastasize at an early stage. Therefore, people over 40 years old should suspect malignant melanoma if black nodular damage occurs on normal skin or mucous membrane, or if the original junctional nevus suddenly enlarges to more than 1 cm, or if the skin becomes rough, ruptures, bleeds and changes in color. However, because skin cancer starts insidiously and develops slowly, it is sometimes easily confused with some common benign new skin organisms. Some careful people may be disturbed by the appearance of some benign skin neoplasms. Therefore, it is necessary to recognize them properly. 6.Nevus, or pigmented nevus, refers to a dark neoplasm that is not visible at birth but manifests itself during childhood and adolescence. Medically, there are two kinds of nevi, one is called junctional nevus, which means that the nevus cells are located in the bottom layer of epidermis and the upper layer of dermis. This type of nevus occurs mostly on the palm, metatarsal, genitalia or trunk, usually only a few millimeters in diameter, with a smooth, hairless, slightly elevated skin surface, and brown or dark brown color. It can fade on its own after puberty, or it can develop deeper to form an intradermal nevus. Another kind of intradermal nevus, mostly found on the face and neck of adults, is a dome-shaped papillary elevation that can range in color from normal skin tone to dark brown and can contain hair, usually the size of a pea to a cherry. In addition to affecting aesthetics, internal nevi are extremely benign and do not become malignant. On the contrary, junctional nevus may become cancerous if it occurs in the palmoplantar area under pressure or in the area where the waist and shoulders are prone to friction. At this time, the original nevus enlarges, bulges, darkens, ruptures, bleeds or satellite nevus appears around it, which are all signs of malignant transformation and should be alerted. Various kinds of skin cancers tend to occur in middle-aged and elderly people above 40 years old, but because of the slow development of skin cancer, patients in the middle and late stages should not give up the chance of eradication arbitrarily, because even patients with recurrence can still get more than 70% of five-year survival rate.