How Much Sun Exposure Do You Really Need? Insights from a GP

Sunlight plays an important role in everything from vitamin D production to sleep, mood and overall wellbeing. However, with so much conflicting advice around sunscreen, UV exposure and getting enough vitamin D, it can be difficult to know what is actually best for your health. 

According to Dr. Kaywaan Khan, the key is not avoiding the sun altogether, but understanding how sunlight changes throughout the day and adapting your habits accordingly. Here’s what you need to know about getting the right amount of sun exposure while protecting your skin. 

How Does Sunlight Change Throughout the Day? 

The mistake I see most often is patients judging sun risk by temperature rather than the UV Index. A cool, overcast morning can carry a higher UV Index than a warm afternoon because UV intensity is influenced by the angle of the sun, not by how hot it feels on the skin.   

UV, or ultraviolet radiation, is a form of energy emitted by the sun that can damage skin cells, causing sunburn and, over time, increasing the risk of skin cancer. It builds throughout the morning, peaks around midday when the sun is highest, and eases off again in the afternoon.   

Early in the day, UV levels are usually much lower, making it a safer time to enjoy being outdoors. Routine sunscreen may not be necessary unless you are spending prolonged periods outside, at high altitude or near reflective surfaces such as water. However, in some countries, the UV Index can already reach moderate levels by mid-morning, so it is worth checking rather than assuming.   

The UV Index removes much of the guesswork by showing the intensity of ultraviolet radiation at a particular time and, therefore, the level of potential skin damage. It does not tell you whether it is a good time to be outdoors, but it can help you decide what protection may be needed. I encourage patients to check it in the same way they would check the weather forecast, rather than relying on instinct alone. 

How Much Sun Do You Need for Vitamin D? 

Unfortunately, there is no single figure I can give here. Two people standing in the same garden for 20 minutes can end up with very different vitamin D levels, because it depends on skin tone, age, where they live and the time of year. Someone with fairer skin has less melanin, so more UVB reaches the skin and vitamin D synthesis happens faster. Someone with darker skin needs considerably longer in the same conditions to produce the same amount. 

During a UK winter, getting enough vitamin D from sunlight becomes far more difficult. Between roughly October and March, UVB rays at this latitude are generally too weak for the skin to produce meaningful amounts of vitamin D, regardless of how long you spend outdoors. Sunscreen and full-length clothing in winter, both of which I recommend without hesitation, can reduce vitamin D production further by limiting the amount of UVB that reaches the skin. This is why I often discuss supplementation with patients in these circumstances, as it offers a safer and more reliable way to maintain adequate vitamin D levels without increasing unnecessary UV exposure. 

We are also increasingly learning that sunlight does more than simply help us produce vitamin D. Research suggests it may influence cardiovascular health through nitric oxide release, support immune regulation, improve mood via circadian pathways, and potentially affect metabolism and mitochondrial function. However, many of these areas are still being actively studied, and the current medical consensus remains unchanged: enjoy regular time outdoors, prioritise natural daylight in the morning and continue to protect your skin from sunburn. 

Why Is Morning Sunlight Important for Your Circadian Rhythm? 

If there is one piece of advice I would want every person to take away, it is this: getting five to ten minutes of outdoor light in the morning is one of the most effective habits for supporting alertness during the day and better sleep at night. That short window of morning light is one of the strongest cues the body has for resetting its internal clock, signalling directly to the brain that the day has begun. 

Standing by a window generally does not have the same effect, and this catches many people out. Glass filters some of the light the brain relies on to regulate the sleep-wake cycle, while indoor light is usually far less intense than the light outdoors. Even on a cloudy day, stepping outside gives the brain a much clearer signal than sitting in a bright room. 

Evening habits matter just as much as morning ones. Bright artificial light, particularly from phones and laptops, can delay the release of melatonin, the hormone that helps prepare the body for sleep. This can confuse the internal clock about what time it is. 

I recommend switching off screens and bright overhead lighting around an hour before bed and moving instead to candlelight or very warm, dim lighting. It may seem like a small change, but it helps sharpen the contrast between day and night that the circadian rhythm depends on. 

How to Get Safe Sun Exposure in the Summer 

The goal is to enjoy sunshine safely, rather than avoiding it altogether. 

Once the UV Index reaches 3 to 5, start thinking about sun protection, particularly if you will be outside for more than about 20 to 30 minutes. Fair-skinned individuals can burn surprisingly quickly, so I would recommend wearing a hat and sunglasses and diligently applying SPF 30+ if outdoors for extended periods. 

At a UV Index of 6 or above, lighter skin can burn in as little as 15 to 25 minutes, so try to limit prolonged direct sun exposure. Here, it becomes more important to seek shade around the middle of the day and wear broad-spectrum SPF 30+ and protective clothing. 

When the UV Index reaches 8 to 10, this is where I become much more cautious, as burns can develop in as little as 10 to 15 minutes in susceptible individuals. Avoid deliberately sitting or lying in direct sun, particularly between approximately 11am and 3pm. Outdoor activities are still absolutely fine, but they should be undertaken with good sun protection and regular shade breaks. 

The UK rarely experiences a UV Index of 11 or above. However, if you are travelling to Australia, the Middle East or other tropical regions, this level of UV is much more common. I would strongly advise avoiding unnecessary sun exposure during the middle of the day. If you do need to be outside, use multiple protective measures, such as walking in the shade, applying broad-spectrum SPF 50+ every two hours, wearing UPF clothing, a wide-brimmed hat and sunglasses. Wherever possible, schedule outdoor activities for the early morning or late afternoon. 

Ultimately, the aim is to find the right balance with sun exposure. Natural daylight supports many aspects of our wellbeing, and spending regular time outdoors should be part of a healthy lifestyle. The important part is adapting your sun protection to the conditions, so you can enjoy the benefits of being outdoors while avoiding unnecessary UV damage.