There are implicit social rules about borrowing things from roommates. I will ask my roommates if I can borrow one of their tomatoes for a recipe, but I won’t hesitate to use their garlic powder without asking. Life would be so tedious if every roommate had to buy their own eggs that only they could use, crowding up the fridge with four egg cartons. When it comes to the basics, any rational roommate is okay with sharing. If they’ve got you this time,  you’ll get them next time. 

In my opinion, the basics usually don’t include expensive beauty products. I will always let my roommates or their houseguests borrow my hairspray or hair dryer when they need it, but there’s no way they’re going to use my exorbitantly expensive shampoo for blondes. If they were having a blonde emergency, I would offer it, but under normal circumstances, that’s totally unnecessary.