Wot screen man said. Any sink will *obviously* only block by what goes down it.
A lot is unavoidable, skin oils etc, but a lot is definitely avoidable IMO, and it's always worth cleaning the trap out regularly too.
Professionally we don't really advocate chemicals anyway, but between me and you I do use a product called One Shot Drain Cleaner at home. It's not available from supermarkets. B&Q sell it but it's quite expensive. I get it from a local hardware store that's about half the price of B&Q.
LINKY for reference purposes.
Note: do not use if you are on a septic tank system.