School biology lessons can sometimes be a case of a teacher trying to impart the basic facts about sex to a group of giggly teenagers. And while the trusty basics are a great place to start, there is so much more about penises and erections that we bet they didn’t teach you. Our sexual health is something we should be all clued up about and our favourite Instagram doctor, Dr Danae Maragouthakis, knows all there is to know about genitals .

We’ve already covered penis misconceptions , now it’s the time for the hard facts...

There are three types of erection If you get an erection you may not think much about how you actually became aroused. But when your penis gets hard, according to Dr Maragouthakis, there are actually three different categories of erection it can fall into. A subconscious erection is the first type.

These hard ons usually occur when you’re dreaming – you won’t need physiological or physical stimulations. Sign up to The Hook-Up, Metro's sex and dating newsletter Love reading juicy stories like this? Need some tips for how to spice things up in the bedroom? Sign up to The Hook-Up and we'll slide into your inbox every week with all the latest sex and dating stories from Metro. We can't wait for you to join us! Psychogenic erections are the result of sexual fantasies either fulfilled in reality or in porn, where your body responds to visual stimuli.

The third and final type of erection is the reflexogenic erection. This is an erection which happens be.