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Evidence Based

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Your Guide to Safe & Healthy Sun Exposure

Written by Dr. Ruscio on September 19, 2023

Written by Dr. Ruscio on September 19, 2023 — Reviewed by Kellie Blake

• What is Healthy Sun Exposure|
• Health Benefits of Healthy Sun Exposure|
• Sun Exposure and Gut Health|
• Seasonal Affective Disorder|
• Sun Safety|
• We Need Sunlight|

I’ll be the first to admit that advice on “what’s healthy” can get pretty confusing and contradictory, and what constitutes healthy sun exposure is no different. By now, we’re pretty well-versed in examples of trendy and eventually debunked/contradictory diet advice: avoid cholesterol (older advice), it’s vital for hormonal health and doesn’t lead to high LDL numbers (newer advice). Certain foods have historically been wrongly vilified, and today I’m going to argue that sun exposure falls into the same camp as those wrongly vilified foods.

When it comes to the big firey ball in the sky, there’s a surprising amount of conflicting information and incomplete advice circulating the internet and even among dermatologists. There’s advice to avoid all forms of unprotected sun exposure, and there’s advice to stand outside at noon in the nude for up to 20 minutes for maximum vitamin D production. These are obviously extremes, but I use them to illustrate my point.

We know there’s a link between chronic sun exposure — particularly sunburns — and skin cancer, but it’s also true that the sun is our very best way to get the vitamin D we need to stay healthy. Vitamin D is vital for mood stability, immune system health, bone health, energy levels, cardiovascular health, and so much more.

Furthermore, there’s compelling evidence that healthy sun exposure can improve the gut microbiota, which is linked to a healthy immune response, digestive health, nutrient absorption, and more. So where’s the middle ground, and how do we find it? How much is too much sun exposure, and how do we know if we’re not getting enough?

What IS Healthy Sun Exposure?

Much like other aspects of a healthy lifestyle, the definition of healthy sun exposure isn’t the same for everyone (how much food is too much? how much exercise is too much? how much sun is too much? — these all vary from person to person, context to context. And in the case of sun exposure, where on the globe you live plays a role too).

Healthy sun exposure for those with darker skin will be longer (in minutes/hours) than for those with paler skin. The Standard Erythemal Dose (SED) is the average dose of sunshine (ultraviolet radiation or UV light) required to cause reddening of the skin (sunburn) and is a key component in helping you determine what a healthy amount of sun exposure is for you [1, 2]. The amount of melanin (pigment) in the skin seems to determine how much UVB radiation can get through the skin to form vitamin D.

Limited evidence has found that the darker the skin, the more melanin, and the less UVB can easily penetrate to make vitamin D. However, one recent study found that the actual differences in vitamin D production were smaller than expected between people with extremely dark and light skin [3].

The tone/color of your skin is called skin phototype and ranges from I – extremely sensitive/always burns to VI – very resistant/almost never burns. The higher the number, the more pigment/melanin your skin has and the greater natural protection you have from the sun’s rays. I’ll use skin phototype, skin type, and phototype interchangeably throughout this article.

The risk of skin cancer associated with chronic UV radiation exposure (especially basal cell and squamous cell carcinoma) is heightened with greater frequency and severity of sunburns (severely damaged skin cells), so those who are on the lower end of the skin phototype scale are at increased risk than those on the higher end. Melanoma, the most deadly type of skin cancer, is associated with too much sun exposure (ie sunburns) at a young age and has additional risk factors, including genetics [1, 4, 5].

Importantly, this is not to say that those on the lower end of the skin phototype should avoid sun exposure entirely. It’s just to say that their healthy levels will be a lot shorter, and likely need to be at more specific times of day.

The trick to healthy sun exposure is to consider [1]:

• Your skin type
• Current vitamin D levels in your blood
• Where you live (latitudinally)
• Time of day
• Cloud cover and other atmospheric conditions
• Ozone thickness
• Time of year

Admittedly, that’s a lot to consider and not really a trick. Most people don’t know their current blood levels of vitamin D levels or what the ozone thickness is where they are at any given time. You do know your latitude, time of year, and skin type though. 

Latitudinally, the closer you live to the equator, the more directly penetrating the sun will be. If you live in a tropical or subtropical place, you will likely have access to adequate sun exposure year-round. In places north of that, if you don’t get adequate sunlight in the winter, you might consider investing in a light box/light therapy lamp designed to help ward off seasonal affective disorder.  

Let’s look at what the research says about skin type.

Research suggests that people with darker skin (phototype V) need about 25–40 minutes of daily sun exposure (without sunscreen) on 35% of their skin (hands, face, forearms, and lower legs) at lunchtime from March to September to produce enough vitamin D [6].

Lighter-skinned people (phototypes I–IV) need about 9 minutes of daily sunlight (without sunscreen) on 35% of their skin (hands, face, forearms, and lower legs) at lunchtime from March to September. If this is hard to achieve during springtime and fall, they can spend about 13 minutes with their hands, face, forearms, and lower legs exposed each day from June to August [6].

Unfortunately, the authors didn’t calculate for people with the darkest skin (phototype VI), and there are not yet reliable recommendations for people with this phototype [4]. Until we have research directly calculating the amount of sun exposure people with skin phototype VI need to maintain adequate levels of vitamin D, it may be safest for VI phototypes to follow the recommendations for type V skin, have their vitamin D levels checked periodically, and then adjust accordingly. 

Vitamin D deficiency is very common among Black Americans and Black Canadians, so getting checked is important, and more research is needed for those with the darkest skin types so that they can have proper information tailored to their specific needs [7].

I had an enlightening conversation with Dr. Michael Holick, a global authority on the topic of healthy sun exposure and Vitamin D levels. We talked about the correlation between sun exposure and reduced risks of certain cancers as well as his opinions on the dangers of tanning beds, why you should protect your face, and how to balance sun exposure with photoaging risks. You can listen to our conversation here.

The UV Index

Though it isn’t perfect, the UV Index is a useful scale to help each of us figure out how much time we should spend in the sun at different times of day to avoid burning. You can find apps for your phone that show the UV Index for your location and time of year.

If you want to find specific limits for your body, you may refer to the above chart and start by exposing daily about 10% of your skin (face and forearms, for example) [8] to midday sun for the lower limit of time before burning, per your skin phototype. Then, you can periodically check your vitamin D levels and add or subtract time and/or amount of skin exposed based on that.

Health Benefits of Healthy Sun Exposure

Sun exposure is required for the production of vitamin D in your body. Certain foods contain vitamin D, and there are supplements, but obtaining vitamin D from regular, healthy (non-burning) doses of sunshine may be the optimal way to get most of our vitamin D requirements.

That’s because the body self-regulates its levels, manufacturing more vitamin D initially to replenish low levels after winter, and slowing down once levels become optimal. Unlike oral vitamin D supplements, vitamin D made from sunlight cannot reach toxic levels in the body. Vitamin D is a fat-soluble vitamin, which means that your body holds on to the excess, leading to the possibility of overconsumption [8]. (Water-soluble vitamins taken in excess get excreted through urine.)

Vitamin D is a key nutrient in many systems of the body. It regulates calcium and phosphorus absorption in the gut and helps the kidneys reabsorb these minerals to maintain healthy bones and muscles [9]. It also helps with insulin production, heart contractions, immune system function, and preventing inflammatory bowel diseases [9].

Maintaining healthy levels is critical, as deficiencies are associated with a number of diseases and ailments. The most common issues are osteoporosis, muscular pain, and a higher risk of fracture, but rare conditions like rickets in children and osteomalacia (bone softening) in adults are also possible (mostly in developing countries at this point in time) [10].

A meta-analysis looked at eight studies and found that [3]:

• Vitamin D deficiency and insufficiency were significantly associated with a higher risk of Parkinson’s disease.
• Sunlight exposure (≥15 min/week) was significantly associated with a lower risk of Parkinson’s.
• Vitamin D supplements increased vitamin D levels but had no real effect on motor function in Parkinson’s patients.

But the benefits of sunlight (specifically UV exposure) go beyond making vitamin D. Year-round and wintertime sun exposure was shown to prevent wintertime vitamin D deficiency in 95% of white adults and 83% of white teens in a recent UK study [6]. To reiterate, people with darker skin might need to increase their relative sun exposure or consider taking vitamin D if their levels are low during winter months, especially at higher latitudes (about 40° N or S). 

UV Exposure Benefits Beyond Vitamin D

Historically, the medical establishment has associated the benefits of sun exposure directly to vitamin D levels, but studies comparing vitamin D supplementation to UV exposure seem to indicate that supplementation doesn’t yield the same results. Other effects of sun exposure include:

• Formation of nitric oxide, which may improve cardiovascular health [1]
• Formation of prostaglandin E2, which may improve immune function [1]
• Temporary suppression of the immune system (may reduce symptoms in autoimmunity but can inhibit immune responses to infections, vaccines, and cancerous skin lesions) [1]
• Reduction of high blood pressure [11]
• Reduction in dementia-related restlessness and tension [12]
• Possible lowered risk of:
  • Cardiovascular disease [11]
  • All-cause death [11]
  • Type 2 diabetes [8]
• Possible improvements in gut microbiota [13, 14, 15]

For these reasons, getting vitamin D from sun exposure is definitely the preferred method, but if levels are too low and safe sun exposure isn’t an option, it’s still not a bad idea to consider supplementation to bring levels up to normal.

Sun Exposure and Gut Health

The connection between the skin and the gut (the gut-skin axis) is a well-documented and medically established phenomenon. Trouble with the gut is often reflected in the skin in the form of acne, eczema, rash, rosacea, and other skin sensitivities. But there also seems to be compelling research that sun exposure to your skin may also affect your gut.

A 2019 study looked at whether exposing the skin to UVB light to increase vitamin D levels would also affect the composition of gut microbiota. It was a small study of 21 healthy women, some of whom had taken vitamin D supplements the previous winter. The findings showed that women with low vitamin D levels had significant changes to their gut microbiota in response to UVB exposure, and that change actually helped raise their vitamin D levels [16].

Researchers then compared those changes in the gut microbiota to that to modern communities that engage in a hunter-gatherer lifestyle and posited that the higher levels of Proteobacteria (a gut bacteria) in sun-exposed individuals indicate the power of sun exposure for modulating the gut microbiome [14].

Medical science also recognizes a gut-skin-immune system connection. A literature review examining the interplay between skin conditions, the immune system, and the gut microbiota found that probiotics can improve acne, psoriasis, and eczema, and that gut conditions often go hand-in-hand with skin diseases. Furthermore, exposing the skin to UVB to increase vitamin D levels can increase the diversity of the gut microbiota, and in psoriasis patients can change the skin microbiota [15].

Seasonal Affective Disorder

If you’ve ever lived in a place that loses sunlight for significant parts of the year, you may have experienced seasonal affective disorder (SAD). This mental health issue feels very much like depression — lethargy, general malaise, and a loss of your sense of well-being. This is due, in part, to a lack of vitamin D production during those sunless or low-sun months of the year. Sun exposure (and even tanning beds and sun lamps) reduces the likelihood of experiencing SAD.

A randomized controlled trial found that for women with osteoporosis and insufficient vitamin D, getting 30 minutes a day of UVB from a tanning bed for 2 weeks significantly improved their vitamin D levels, though it did not help with bone formation [17]. Importantly, the studies comparing sun exposure and light therapy to vitamin D supplementation showed that vitamin D supplements did not have the same effect as light exposure [18].

Without adequate daily sun exposure during certain parts of the year (and for certain people), circadian rhythms can be disrupted, which can create problems with mood and your overall sense of wellness. Serotonin, a “feel-good hormone”, is a precursor to melatonin, which helps us fall asleep at night. With normal physiology, sunlight suppresses the release of melatonin in the morning and stimulates the release of serotonin. Limited sunlight during the winter months means less serotonin and more melatonin, and the altered production of these hormones is implicated in developing SAD and depressive symptoms [19]

Using a sunlamp first thing in the morning during winter months has been shown to at least partially alleviate seasonal affective disorder [19]. Furthermore, the literature review I’ve cited here found that bright light therapy may have utility for improving mental health beyond SAD, to include treatment for other mental health disorders. Bipolar depression, non-seasonal unipolar depression, eating disorders, and adult ADHD all seemed to show improvement with the use of light therapy.

Sun Safety

I can’t complete this article without acknowledging the very real risks of prolonged unprotected sun exposure, not just to your skin, but to your eyes. Sun damage is very real, and it goes beyond vanity and wrinkles. The risk of skin cancer and eye diseases like cataracts and macular degeneration is dramatically increased with excessive exposure to the sun’s rays [1].

While I’m directly advocating that individuals of all skin phototypes spend time outside without sunscreen to reap all the health benefits of sun exposure, that time should be deliberate and limited, and you should listen to your body. And if you’re particularly sensitive or have a sun allergy, you should most certainly follow the advice of your healthcare provider on this topic.

As you saw above, many of the recommendations for sun exposure involve exposing your face. However, in many cases, sun exposure to the face comes with its own additional concerns and may not be the best place to rely on for receiving sunlight unprotected. Here are a few things to consider: 

• Melasma: a skin condition characterized by brown or blue-gray patches or freckle-like spots (hyperpigmentation), sometimes called the “pregnancy mask” that can result from sun exposure to women’s faces. The risk of melasma is greatly increased for women on birth control, specifically. 
• Certain skin conditions like acne, rosacea, and autoimmune rashes like in lupus can make sun exposure more likely to inflame facial skin or cause scarring in the case of acne vulgaris.
• Use of certain medications like birth control and mood stabilizers can make skin more sensitive to the sun and more likely to burn.
• Use of topical skin treatments (for acne and anti-aging) like retinoids or tretinoin also makes skin more sensitive to sunlight and more likely to burn.

Exposing your face isn’t mandatory to reap the benefits of sun exposure. And in my conversation with Dr. Michael Holick, he specifically advises against it, and he advises to protect the backs of your hands with SPF 30 or more as well. 

Appropriate sun protection is critical for you to safely enjoy outdoor activities. Use sunscreen with an SPF of at least 30. Wear sunglasses, glasses, or contact lenses with 99–100% UV protection and a hat to protect your eyes on sunny days and at peak sunshine hours [1]. Consider lightweight UPF clothing, which may actually be more protective than sunscreen—and can surprisingly keep you cooler than exposing your bare skin to the hot sun, especially in dryer climates [20]. UPF stands for ultra-violet protection factor and is the measure used for clothing the same way SPF (sun protection factor) is used for sunscreen.

We Need Sunlight

I hope this information has helped motivate you to start spending more time in the sun. Start small, and use the charts in this article to help you figure out what your skin phototype is so that you can safely begin experiencing all the benefits of healthy sun exposure. Don’t stay in the sun long enough to burn. Avoid full exposure in the late morning to mid-afternoon if you have the fairest skin type. Always protect your eyes.

We would love to help you get started on your journey to safe and healthy sun exposure. Reach out to our clinic for more information and to book an appointment.

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