Hives occurs when the body reacts to an allergen and releases histamine and other chemicals from under the surface of the skin. The histamine and chemicals cause inflammation and fluid to accumulate under the skin, causing wheals.

Examples of known Hives triggers

  • Medications, including some antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ACE inhibitors, used for high blood pressure.
  • Foods, such nuts, shellfish, food additives, eggs, strawberries, and wheat products
  • Infections, including influenza, the common cold, glandular fever, and hepatitis B
  • bacterial infections, including urinary tract infections and strep throat
  • Intestinal parasites
  • Extreme temperatures or changes in temperature
  • High body temperature
  • Pet dander from dogs, cats, horses, and so on
  • Dust mites
  • Cockroaches and cockroach waste
  • Latex
  • Pollen
  • Some plants, including nettles, poison ivy, and poison oak
  • Insect bites and stings
  • Some chemicals
  • Chronic illness, such as thyroid disease or lupus
  • Sunlight exposure
  • Water on the skin
  • Scratching
  • Exercise

In over half of all cases, people never find the exact cause.

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