Most people don't know this but wearing caps all the time, especially in places or during times of extreme heat may result in hair loss, or expedite their genetic predisposition to baldness.
Basically, the hair follicles get fried by the intense heat so you lose hair. And so, to prevent hair loss, wear breezy hats like sombreros instead or just use umbrellas. Bandannas will also allow your head to breathe better than caps.
If helmets are necessary in your place of work (like my Dad as a seaman before working on engines), make sure you remove the helmet as soon as possible to let your head breathe.