Sorry boys, we have some bad news.
Penises can actually shrink by up to one inch, and there are a few different reasons why.
You can't do much about some of the causes, but others are completely avoidable if you just change a few simple things.
The average penis size is 13.12cm long with a girth of 11.66cm when erect, but there are five things that could change this.
However there are five things that could lose you some of those precious centimetres, reports the Sun.
Surely this has to be up there when it comes to reasons to ditch the fags.
Some of the toxins in cigarettes can damage the blood vessels in the penis. And that's not the only bad news, smoking can also mean you struggle to get an erection.
Some medicines, particularly those used to treat prostate problems can cause the penis to shrink.
It's also been reported as a side-effect of some antidepressants and antipsychotics.
Okay, so there isn't much you can do about this one.
The penis and testicles can shrink as men get older because the build-up of fatty deposits in the arteries reduce blood flow when you need it.
4. Prostate surgery
About 70 per cent of men who have had surgery to remove the gland because of cancer experience shrinking.
Doctors don't really know why this is.
5. Peyronie's disease
The condition causes the penis to curve when erect but it can also lead to scar tissue which can block blood flow and make it smaller while erect.