Urticaria, commonly known as hives, is not contagious. It is a localized edema of the skin and mucous membranes due to temporarily increased vascular permeability. Its pathological causes are not related to infection, thus it is not contagious. The specific cause of urticaria often remains unclear for many patients. Some cases are due to certain foods, such as animal proteins, seafood, fungi, and some food additives like tartrazine, balsam of Peru, and sulfites. Some cases are triggered by drugs such as penicillin and various vaccines. Others are caused by allergens inhaled through the respiratory tract or by contact with the skin; common examples include pollen, animal dander, dust, fungal spores, and dust mites, as well as some volatile cosmetics. Contact with certain items, such as insect bites, venomous insects, certain plants like nettles, or animal fur such as wool, can also trigger urticaria. Some cases may be related to physical factors such as exposure to cold, heat, sunlight, or pressure, all of which can potentially lead to the development of urticaria.