What makes ant bites itch?

Skin reaction: The chemicals from the bites of ants cause a reaction in your skin, which causes the itching. Medications, like diphenhydramine, (benadryl in the US) block part of this reaction and can provide relief. Corticosteroids (like hydrocortisone) applied to the skin can also block another part and provide relief as well.

Histamine: Bug bites tend to itch because they leave behind some extra saliva or other products from their biting apparatus. These substances are recognized as foreign material by your body, which mounts an inflammatory response to mobilize cleanup and infection control. A key component is histamine, which increases flow to that area (red welt) and itches. Histamine is the same stuff that causes hives.

Histamine: Ants release a chemical called formic acid when they bite. As this is an irritant, our bodies release histamine at the site of the bite which causes itchiness.