During sexual arousal, blood flows into spongelike spaces inside the penis, making it expand and become stiff. A bent penis tends to happen when these spaces don't expand evenly. Most often, this is due to common differences in penis anatomy. But sometimes, scar tissue or another problem causes a bent penis and painful erections.

Causes of a bent penis can include:

• Changes before birth — Some people are born with an issue that causes the penis to curve when erect. Often, it's due to a difference in the way certain fibrous tissue inside the penis develops.
• Injuries — The penis can get fractured during sex or injured from sports or other accidents.
• Peyronie disease — This happens when scar tissue forms under the skin of the penis, causing erections to bend. Penis injuries and certain urinary tract surgeries can raise the risk of Peyronie's disease. So can some conditions that affect connective tissue and certain diseases in which the immune system attacks healthy cells.

Sometimes, a penis can curve to the side, upward or downward when it's erect. This is common, and a bent penis usually isn't a problem. Most often, it's only a concern if your erections are painful or if the bend in your penis causes problems with sex.

A bent penis often doesn't need treatment. But if it causes pain or keeps you from having sex, call a doctor or other health care professional. You might need to see a doctor called a urologist, who diagnoses and treats sexual and urinary problems.