Use the adjective bald to describe someone who has no hair on his head. If your uncle has a smooth, hairless scalp, he's bald.
Some men are bald because they shave their heads, while others have become bald gradually over the years. It's often said that if a man's grandfather was bald, he will also be bald. Certain conditions, illnesses, and even medicines can also make women bald. Another way to use the word is to mean "plain, blunt, or obvious." You might describe, for example, a school's bald request for donations of money and supplies.