Butthole sunning, more formally called perineum sunning, is the practice of exposing your perineum (the area between your genitals and anus) to direct sunlight. It went viral in late 2019 after Instagram posts claimed that just 30 seconds of sunlight on the perineum was equivalent to a full day of regular sun exposure. There is no scientific evidence supporting any of those claims.
Where the Trend Came From
The practice gained mainstream attention in October 2019 when wellness influencers began posting photos of themselves lying on their backs with their legs spread toward the sun. Posts claimed the technique was rooted in ancient Taoist practices, specifically the concept of the “Hui Yin” point, an acupressure point located at the perineum that some traditional Chinese medicine practitioners consider a gateway for energy. In the wellness version of the idea, exposing this point to sunlight was said to “charge” the body’s energy reserves.
The trend spread quickly. A study published in JMIR Dermatology tracked the surge in public interest and cataloged the specific claims circulating online: that perineum sunning would improve focus, boost libido, regulate hormones, enhance longevity, and fix circadian rhythm problems. The authors found no human evidence supporting any of these claims for this specific body area.
What Proponents Claim
The most dramatic claim is that 30 seconds of perineal sun exposure delivers more vitamin D than an entire day of sunlight on your arms and legs. Proponents also say the practice increases energy, improves sleep quality, balances hormones, and strengthens sexual function. Some describe feeling a noticeable “warmth” or energy shift after a session, which they interpret as validation that the technique works.
None of these claims hold up to scrutiny. No study has ever shown that perineal skin generates more vitamin D than skin anywhere else on your body. The benefits people attribute to the practice, like increased energy and better sleep, are well-documented effects of general sunlight exposure. As dermatologist Susan Bard has noted, those benefits come from short sun exposure regardless of which body part you expose. There is nothing special about the perineum in this regard.
Why the Skin There Is Actually More Vulnerable
The perineum and surrounding area are not well suited to direct UV exposure. Skin thickness varies significantly across the body, and the skin in this region rarely, if ever, sees sunlight. That means it has essentially no baseline UV tolerance or protective tan.
Research on epidermal thickness shows meaningful differences between body sites. Buttock skin has a thinner outer protective layer (the stratum corneum) than forearm skin: about 14.9 micrometers versus 18.3 micrometers. That outer layer is your primary physical barrier against UV radiation. While the deeper cellular layer of buttock skin is actually thicker than forearm skin, it’s the outermost layer that determines how quickly UV light penetrates and causes damage. The perineum itself, which is mucosal and transitional skin closer to the genitals and anus, is even thinner and more delicate than buttock skin.
Skin that has never been exposed to sunlight burns faster and more severely. Applying UV radiation to an area with no melanin buildup and a thinner protective barrier is a straightforward way to get a painful sunburn in a place you really don’t want one.
Actual Risks
The most immediate risk is a sunburn on extremely sensitive tissue. Unlike burning your shoulders, a perineal sunburn can make sitting, walking, and using the bathroom genuinely miserable for days.
Beyond the short-term discomfort, UV exposure is the primary driver of skin cancer. Melanoma can develop on any skin surface, including areas that rarely see light. Deliberately exposing a typically covered area to concentrated UV adds risk with no documented benefit. The genital and perianal region is also home to delicate mucous membranes that are more permeable to damage than regular skin.
There’s also a practical concern: most people doing this outdoors are fully exposed, often on a balcony, rooftop, or backyard. Depending on where you live, that could create legal issues around public nudity.
What Actually Works for the Claimed Benefits
If you’re looking for the benefits that perineum sunning promises, there are simpler and safer ways to get them. Morning sunlight exposure on your face, arms, or legs for 10 to 15 minutes helps regulate your circadian rhythm and supports vitamin D production. That’s the same mechanism proponents are describing, just without the unnecessary genital involvement.
For low energy or poor sleep, consistent morning light exposure is one of the most effective non-pharmaceutical interventions available. Sunlight hitting your eyes (not staring at the sun, just being outdoors) signals your brain to calibrate its internal clock. This is the actual biological pathway for circadian rhythm regulation, and it runs through specialized receptors in your retinas, not through your perineum.
For vitamin D specifically, exposing your forearms and lower legs to midday sun a few times a week produces meaningful amounts. If you’re deficient, a supplement is more reliable than any amount of strategic sunbathing.