Hives are red, itchy welts. Heat hives are more accurately described as heat rashes or cholinergic urticaria. They can develop after activities that raise your toddler's body temperature. Your toddler can develop these hives after a hot bath, if he sat too long in the sun, if he is wearing tight-fitting clothes or when he is running a fever. This hypersensitivity to heat can also be trigger by sweat or spicy foods.
The exact causes of heat hives are still unknown. Different studies indicate that it could be a form of autoimmune response to sweat or a blood disorder with an allergy component. However, heat hives are known to involve the neurotransmitter acetylcholine. When your toddler's body temperature increases, the mast cells in the skin break down just before sweating starts. This breakdown is triggered by acetylcholine and, in turn, triggers the release of histamine, which is responsible for the appearance of hives on the skin.
Signs and Symptoms
Heat hives starts with itching or stinging in the limbs, back, chest or face before spreading all over the body. If your toddler's body temperature is not brought down immediately, the itch can get worse and produce a burning sensation on the skin. Soon the skin turns red and forms swollen spots when scratched. Finally, the ability to sweat, and thus to cool down, decreases greatly.
The first-line drug for heat hives is antihistamines such as children's diphenhydramine. However, consult your toddler's pediatrician before starting him on the drug. Prevention is a better approach. It involves reducing your toddler's exposure to known triggers of heat hives, including direct sunlight, tight clothing, hot baths and hot food. Rarely heat hives may progress to anaphylactic shock involving severe swelling. If your child is having difficulty breathing, seek medical care immediately.
Changes in Sensitivity
Your toddler may show varying sensitivities to the triggers of heat hives at different times. This variation may be seasonal or occur in longer cycles. In some cases, sensitivity to heat can go on continuously for a few years before resolving, or appear and disappear over many years.