The Sun emits ultraviolet radiation that has a positive health affect.
It has long been believed that exposure to sunlight allows the body to generate Vitamin D3, which in turn can strengthen bones, promote cell growth, neuromuscular and immune functions, and reduction of inflammation.
While people can consume Vitamin D by ingesting it from diet and supplements, the major natural source of Vitamin D is from the synthesis of cholecalciferol in the lower layers of epidermis of the skin through a chemical reaction that is dependent on sun exposure.
Sunbathing also has other benefits, which include an increase in endorphin levels, and reduce the risks of seasonal affective disorder, among others.
In short, sunlight exposure can improve wellness.
And this time, a number of users on TikTok are pointing their bare buttocks to the sky, in an effort to bring the light to where the sun usually doesn’t shine.
"Perineum sunning" for what it's called, is "like the sunlight fills your being from the bottom up," said one user.
"It’s a feeling you can’t really describe unless you experience it."
The perineum is that small area between the anus and scrotum for male, or the vulva for female.
Located between the pubic symphysis and the coccyx (tail bone), including the perineal body and surrounding structures, the perineum is an erogenous zone, meaning that it has lots of nerve endings.
Proponents of the pubic practice claim that sunlight exposure to the region provides a host of benefits.
"Better sleep, balanced hormones, more energy, higher libido, increased creativity, sweet freedom, [and] a nice tan [butt]," said another TikTok user.
Other influencers have likened the results to a cup of coffee, or to recharging their batteries.
"Thirty seconds is equivalent to walking around with your clothes on all day long," claimed another user.
With the many TikTok users doing the stunt, the #perineumsunning has garnered millions of views on the social media platform.
While doing the perineum sunning can provide a unique experience, considering that the area is located near the genitals and is concealed most of the time, the activity has lots of negative effects.
This is because the Sun's ultraviolet rays are carcinogens.
While the rays do have health benefits, sunlight can also create sunburns.
The toxic effect of ultraviolet rays happen beyond tanning, and can create malignant melanoma, which is mostly caused by indirect DNA damage.
In other words, ultraviolet rays can create skin cancer, among others.
Making perineum sunning worse is that, the skin in the area is sensitive. Because of this, exposing ones' genitals and anus to the sun simply increases the risk of ultraviolet rays damage.
Doctors have weighted, and a number of videos on TikTok also started mocking the trend, soon after the hashtag went viral.
It's worth noting pereneum sunning gained its first popularity in 2016.
Pereneum sunning, or also called "butthole tanning" or "sunning your hole" has since been attempted for several years. But it gained its first viral sensation in 2019, when Instagram user metaphysicalmeagan mentioned the practice, and attracted media attention, including Papermag, Rolling Stone, and Men's Health.