Sudden redness, itching and swelling of the palm of the hand may be due to insect bite reaction, contact dermatitis, eczema and other diseases. 1. Insect bite reaction: the allergen of this disease is the secretion injected by insects when biting human skin, so when the palm of the hand is bitten by insects, local erythema, edema, itching and other manifestations will suddenly appear. 2. contact dermatitis: this disease is caused by contact with exogenous allergens in the palm of the skin, commonly found in rubber gloves, cleaning products, animal dander, soap, paint, etc. Typical lesions for the border of clear erythema, accompanied by swelling, itching, so patients will appear in the palm of the hand suddenly red, itchy and swollen symptoms. 3. Eczema: the cause of this disease is not clear, studies have shown that it may be related to genetics, hormone level disorders, immune function abnormalities, as well as contact with allergens, mental stress, etc., the rash occurs in the head, face, hands, feet, etc., can be seen in redness, itching and other symptoms, manifested in the palm of the hand suddenly red, itchy and swollen. There are other possible causes for the sudden itching and swelling of the palms, such as ringworm, dengue, etc. It is recommended that patients with sudden itching and swelling of the palms go to the hospital, complete the relevant examinations and identify the specific causes.