Men who don't wear underpants have higher sperm quality compared to those whose reproductive organs are tucked away in tight underwear and trousers, according to research in the recent Scottish Medical Journal.

Studies investigating the decline in semen quality have suggested a number of reasons, from living near places with high air pollution, to changes in lifestyle and rising levels of obesity.

There are those who believe men who wear Scottish kilts have better sperm quality and fertility - especially as the traditional dress of Scotland is worn without underwear. The idea seems plausible because in many mammal species, including humans, healthy sperm production requires the temperature of the scrotum to be 3 deg C lower than the body temperature, so perhaps men who wear clothing that keeps that area too warm, may inadvertently be reducing their sperm quality.

This latest review, by Erwin Kompanje of the Department of Intensive Care at Erasmus MC University Medical Centre in Rotterdam in The Netherlands, appears to suggest a way to redress the worldwide decline in human sperm quality.

The Scottish kilt is a male garment that at first glance looks like a knee-length, pleated skirt. It is the national garment for Scotland, where it is worn typically for weddings and other special occasions. There are also moves to introduce the kilt as casual wear, even outside Scotland.

Kompanje notes that according to a recent survey, the vast majority of Scotsmen (about 70%) still choose to wear nothing under their kilts. This is known as the "regimental style".

For his study, Kompanje reviewed all the literature he could find via Medline and the Cochrane Library that looked at scrotal temperature, ability to produce sperm and fertility.

He did not find any evaluations of "therapeutic kilt wearing in relation to sperm quality", and reports he is not aware of any randomized controlled trials exploring the health benefits of kilt wearing, but he does note there are some old anecdotal papers on the pros and cons of kilt wearing.

He did however, find some research reports on the effect of underwear wearing. For example, research done in the 1990s proposed that wearing tight underpants tended to increase the temperature deep inside the scrotum; on average, wearing tight underpants appears to raise the temperature around the testicles by 3.5 deg C.

He also writes that:

"Wearing a kilt has strong psychological bene?ts. A kilt will get you noticed no matter where you are. Research indicates that men wearing a kilt experience a strong sense of freedom and masculinity and that many women are attracted to men in kilts."

From his review, Kompanje concludes that kilt wearing, particularly in the "regimental style" (that is without underwear) likely offers the ideal physical environment for the scrotum, helping to maintain the ideal temperature for the testicles to be able to produce good quality sperm.

He says while further research is needed to confirm this, in the meantime:

"Because the kilt is a purely masculine garment, men need not be ashamed of or reticent about the therapeutic wearing of a kilt for a certain period of time to possibly improve sperm quantity and quality."