How long do mosquito bites itch for?

Days: Usually last for a few days, rarely over week.

Longer if you itch: Them. Itching will go away within days if you don't scratch.

A few days usually: Occasionally, people will have a delayed-type hypersensitivity reaction to mosquito bites. I am one of those people. The initial redness (relatively mild) lasts a day or two, followed by persistent redness and itching that goes on for a week or more. Hydrocortisone cream is your friend under these circumstances.