Polyester underwear in female dogs showed disruption of endocrine hormonal cycles.

“So, the study is the effect of different types of textile fabrics on spermatogenesis, an experimental study. 24 dogs divided into two equal equal groups, one which wore cotton underpants, and the other wore polyester underpants. Seven dogs wore nothing uh and were used as controls. I guess seven dogs were freeballing. Um 12 polyester underwear, 12 cotton underwear. And if you look at the outcome, you'll find that the cotton underwear showed insignificant changes in spermatogenesis. Polyester pants had a deleterious effect on spermatogenesis of the dogs, which was reversible in the majority of cases, but it took some time.”