Most men aren't wearing condoms and now we know why.

Despite everything we know about sexual health, including that condoms are the only form of birth control that protects against the majority of sexually transmitted diseases, most men still aren’t whacking one on before sex.

A recent study found that condom use among Australian single, heterosexual men is on the decline. Only 35 per cent said they’d used a condom during their last casual sexual encounter. Furthermore, a report from the Centre for Social Research in Health determined that less than half of gay or bisexual men always use condoms with partners.

The common complaint has been diminished sensitivity, with men claiming that sex simply doesn’t feel as good with a condom on.

But it turns out there’s far more to the story.

The New York Times reported this week that men aren’t wearing condoms because of a global sizing problem.

Simply, standard condom sizes are far too big for the average penis.

Condoms must be at least 6.69 inches, or 17 centimetres long, despite the reality that the average erect penis is 2.5 centimetres shorter than that.

Sexual health expert Debby Herbenick said that of the 1661 men they studied, 83 per cent had penises that were too short for the average condom.

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As well as being uncomfortable to wear, condoms that are too big can be hazardous. A recent study, which interviewed people between the ages of 18 and 29, found that 48 per cent had experienced a condom slipping off during sex, and 51 per cent had a condom come off during withdrawal.

In response, a Boston-based company has developed a custom brand of condoms called myONE Perfect Fit, which offers no less than 60 different sizes. They vary in both length and circumference.  Within hours of going on sale, CEO David Wedel told the New York Times, that all 6o sizes had been purchased by various customers.

In order to purchase a bespoke condom, men need to download and print a measuring kit from the ONE website. They can order a few sizes to see which one fits best. Currently, they’re only available in the United States, but there are other custom-fitted condom companies that ship worldwide, like My Size, which you can visit here.

Having condoms available that actually fit the consumer seems like a fair place to start when it comes to increasing condom use.