system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do anti-bacterial hand gels/soaps kill bacterial cells but not your own cells?

EDIT: Wow, thanks for the great responses! Never knew epidermal cells were dead... kinda creepy really!
gpt
There are multiple kinds. The alcohol-based gels work by ruining the bacteria's cell walls; alcohol in high concentration is very lethal to nearly all bacteria. The outer layer of human skin is already dead, and a lot more resistant to being penetrated by alcohol; the 30 seconds or so that you're rubbing your hands isn't enough to get through that (relatively) thick layer of protein and other dead-cell bits. But if you get hand sanitizer into a small cut it will touch unprotected, living tissues and sting. It also strips your skin of some of its natural oils, which is why the hand gels usually have moisturizers in them.

Related: Your stomach, and to some extent other parts of the digestive tract, is already protected against *some* chemicals because it's such a strongly acidic environment anyway and it takes rapid cell replacement and a mucus layer to keep the acid from harming you. This also reduces damage from alcohol, though alcohol is still poison. Ethanol, the kind in liquor and beer, is a poison too, but mild to humans in very low concentrations and we've evolved to be able to consume small amounts. It's naturally present in fermenting fruit etc. anyway like we would have encountered in the wild. If you drink a human-potable form of alcohol (say, vodka, which is usually 35-50% ethanol) the most it'll do to your stomach, if you don't overdo it, is irritate the lining; stomachs are tough. Then it's diluted heavily in your bloodstream. But if you wash a countertop with that plain vodka, it'll kill a lot of bacteria; it hits them full-strength and they don't have protective layers. 

The soaps with a small amount of an antibacterial topical drug in them, instead of alcohol, are similar. They're toxic to bacteria, but don't really penetrate the thicker, non-living human skin layer. The amount of exposure you get just from washing your hands, even if you have a few little cuts, isn't enough to do anything bad to you.