Allergic dermatitis is a dermatitis caused by allergens (allergens) through the mechanism of allergic reactions. Allergic dermatitis, also known as allergic dermatitis, is a dermatitis caused by allergens (allergens) through the mechanism of allergic reactions, and is an inflammatory skin reaction caused by many factors. Allergic dermatitis is the most common disease in dermatology. With modernization and environmental changes, exposure to chemicals is increasing, making people significantly more likely to develop allergic dermatitis. Common clinical allergic dermatitis include drug dermatitis, contact dermatitis, photosensitivity dermatitis, genetic allergic dermatitis, self-sensitivity dermatitis, etc. Due to the different causes of allergy, the prevention and treatment methods also vary. Let’s analyze them separately. 1, drug dermatitis Some sensitive patients have allergic reactions to certain drug components that enter the body through various routes and skin symptoms that occur. Once skin symptoms appear within a few hours to 2 weeks after the use of drugs, the first thing to consider is drug allergy, should immediately stop the drug and go to the hospital, ask the doctor to diagnose and treat. After the diagnosis of drug allergy must remember the name of the allergic drug, and must tell the doctor when you visit the doctor in the future to avoid using it, thus leading to re-allergy or even life-threatening. 2. Contact dermatitis is, as the name implies, an allergic reaction at the contact site after contact with certain substances. Common contact allergens include metals (eyeglass frames, belt buckles, watches, alloy necklaces, earrings, etc.), plastics (sandals, ornaments, etc.), cosmetics, adhesive tape, etc. Contact dermatitis is characterized by the onset of the contact site, and some even have the same specific shape as the contact object. However, some contact allergies such as cosmetic allergies are not easily diagnosed and a patch test is required to confirm the diagnosis. For allergic people (people who have had various allergic reactions), it is best to try new cosmetics behind the ear or on the flexor side of the forearm for a few days before using them, if there is no erythema and itching before buying and using them. 4, photosensitive dermatitis is a kind of allergic skin disease that occurs after the skin is exposed to sunlight due to the presence of photosensitive substances. Photosensitive substances can be internal medications (such as tetracyclines, sulfonamides, etc.), food (such as mud snails, gray vegetables, etc.), daily contacts (such as fragrances, preservatives, dyes in cosmetics, detergents, etc.), occupational contacts (such as tar, asphalt, etc.) or endogenous porphyrins, etc. For photosensitive dermatitis, firstly, try to find photosensitive substances and avoid contact or consumption. Next, avoid light by using an anti-UV sunshade and sunscreen. UV shades protect against direct sunlight, but are ineffective against sunlight reflected from the ground and walls, so be sure to use sunscreen at the same time. It is best to use sunscreen with PA++ and SPF15 or more, and a refill at noon, otherwise the sun protection is not effective. 5, genetic allergic dermatitis, also known as atopic dermatitis or atopic dermatitis, is related to genetic allergies, and is characterized by itchy skin, a polymorphic rash and a tendency to exude, with different clinical manifestations at different ages. Patients are often associated with asthma, allergic rhinitis and increased serum IgE. In infancy, vesicles, exudative lesions and crusts appear on the scalp, forehead, neck, wrists and flexors of the limbs. In children, the disease is usually aggravated around the age of 4. The lesions involve the extensor or flexor side of the limbs, often limited to the elbow fossa, N fossa, etc. The rash is hypertrophic and mossy. Pruritus remains intense. In young adults, the rash is more common in the elbow fossa, rouge fossa, extremities, and trunk. The rash is often a generalized dry papule, or a limited mossy plaque. For patients with genetic atopic dermatitis, in addition to internal anti-allergic medications and topical medications, attention should be paid to observing food reactions and avoiding allergenic foods. Pay attention to the detection of environmental factors that aggravate the condition and try to avoid them. Avoid excessive washing and scalding, excessive soap stimulation and excessive scratching, etc. Since the onset of the disease is related to dry skin and decreased barrier function, it is also important to apply topical moisturizer daily.