What is alpha hydroxy and how often should you use it?

It's in many things, lotions, cremes, cleansers, so the use I'm not exactly sure since it is in different products. I do know that you shouldn't use it everyday if you have sensitive skin. Despite the word ';Hydro'; in it, it dries your skin out. Also if you have any cuts, knicks from shaving or raw skin caused by dry skin this ingredient will sting. I was using a firming lotion from Lubriderm once and this was in it, because I had dry skin, even though there were no cuts, it stung a lot. So if you do use it, limit it to every few days or once a week to avoid a red rash like effect from it.