Looks like Superman has some flaws; manly men are more prone to getting the flu.

The Daily Mail reports, new research by scientists at Stanford University in California suggests a buff man's immune system is weaker. This is compared to the immune system of a woman.

It's because testosterone reduces the way the body fights, according to researchers.

One scientist, Professor Mark Davis, believes the reasoning behind the conclusion dates back historically. Men would suffer more diseases and their body had to react when they were known to be the hunter. 

This eventually caused the immune system to overreact. Davis says the manly man's immune system instead decided to fight back against itself.