Bald/Shaved Heads: But Why???

Ok, I have short hair (like Rihanna) but why are women everywhere shaving their heads? Is it too hot outside, did they get a bad cut, are they crazy....??? I have to say that Brittany is not the first and definitely not the last to folly this trend, but usually when a woman shaves her head, something is going on in her personal life that has cause her to go temporarily insane.

La La (Carmelo Anthony)

Cassie (Diddy)

Rihanna (Chris Brown)

Solange (???)

Carmen Elecktra (???)