Hives, also known as urticaria, are itchy, raised welts that appear suddenly on the skin and are usually red, pink, or flesh-colored. They can occur anywhere on the body and may be caused by an allergic reaction to something in the environment or something you ate, or a reaction to an irritant in the environment. Some common causes of hives include:

• Foods, such as nuts, chocolate, fish, tomatoes, eggs, fresh berries, and milk
• Medications, such as aspirin, ibuprofen, high blood pressure drugs, or painkillers
• Insect bites or stings
• Exposure to heat, cold, or pressure
• Stress
• Sunlight
• Infections
• Medical treatments, such as radiation therapy or blood transfusions

Hives can be acute, lasting less than 6 weeks, or chronic, lasting more than 6 weeks. While the cause of acute hives is often easier to identify, the cause of chronic hives is usually harder to identify and may be impossible to find for most people. If you develop hives around your throat or on your tongue or have trouble breathing along with hives, seek immediate medical attention.