Researchers have created a scientific definition of whether a man’s erection can be deemed a “grower” or a “shower”.
They hope that defining which category a man falls into could help make surgical decisions.
According to the study, men whose penis increases in size by more than 56% when erect compared to a flaccid state could be considered growers.
While those who saw an increase in size of less than 31% were showers.
However, most men in the study fell into what scientists described as a “grey zone” in between the two categories.
Only 24% of the men were growers, while a quarter were classified as showers.
Showers also tended to have longer penises when flaccid, the study suggests.
Dr Manuel Alonso-Isa, a urologist at the University Hospital HM Puerta del Sur in Madrid, Spain – who led the study, said: “It is important to be able to predict if a patient is a grower or a shower as when we see them, they are usually in a flaccid state.
“If they grow a lot when they get an erection, it might mean they need a different surgical approach compared to someone who doesn’t grow much.”
The findings are presented at the European Association of Urology (EAU) Congress in Milan.
Urologists based at three hospitals and a clinic in Madrid conducted ultrasound scans on 225 men in both flaccid and then erect states, after giving them an injection.
When they examined the data, the extent of the men’s penis growth followed a pattern that allowed them to set parameters on each category.
The researchers, who also included urologists at the HM hospitals and the ROC Clinic in Madrid, found no link between age, weight, smoking status or other diseases, and penis growth.
But the study found that men who were showers tended to have longer penises when flaccid than growers – an average of 11.3cm compared to 8.8cm.
The research further suggests that the size of the fibrous tissue known as the tunica albuginea, which surrounds the spongy erectile tissue inside the penis, did not predict how much a man’s penis might grow.
But they did find in men who were growers, this tissue became thinner than in men who were showers.
Dr Alonso-Isa, said: “This makes sense as the tissue is being stretched further.
“So it could be that this tissue has more elastic fibres in men who are growers than those who are showers. But we need to do more research to prove this hypothesis.”
He said there may also be other factors they didn’t look at that play a role.
“In the meantime we have defined what constitutes a ‘grower’ or a ‘shower’ in a scientific way, which will be important for the future,” he explained.
Commenting on behalf of the European Association of Urology, Professor Maarten Albersen, a urologist at the University of Leuven, Belgium, said while there may not be any medical consequences to being a shower or a grower, it was something that often weighed on the minds of patients.
He said: “This is a frequent area of concern for our patients and the emphasis should be on normalising baseline and erectile length for all.”
The study, which has not been published in a journal, has not been peer reviewed.