What might cause a horse to have what looks like hives all over?

* Insect bites or stings: Horses can be allergic to certain insects, such as mosquitoes, bees, and wasps. When they are bitten or stung, they may develop hives as a reaction.

* Certain plants: Some plants, such as poison ivy, poison oak, and stinging nettle, can cause hives when they come into contact with a horse's skin.

* Drugs or medications: Some horses may develop hives as a side effect of certain drugs or medications.

* Food allergies: Horses can also develop hives as a result of food allergies. Some common allergens include alfalfa, corn, and soy.

* Environmental allergies: Horses may develop hives as a reaction to environmental allergens, such as pollen, mold, and dust.

* Stress: Stress can trigger hives in some horses.