Sunlight is essential for human health, but too much exposure can be harmful. Experts say people do not need to avoid sunlight completely, but should aim for sensible, regular exposure while protecting themselves from excessive ultraviolet (UV) radiation.
Sunlight helps the body produce vitamin D, which is important for healthy bones and muscles and plays a role in normal immune function. Natural daylight also helps regulate the body's circadian rhythm, supporting healthy sleep patterns and daytime alertness.
Why does the body need sunlight?
UVB radiation triggers vitamin D production in the skin. The amount produced depends on factors including skin tone, age, season, location and the intensity of UV radiation.
Professor Rebecca Mason of the University of Sydney said adequate vitamin D is important for several bodily functions, including bone health and normal immune activity.
Sunlight may also have effects beyond vitamin D. UVA exposure can stimulate the release of nitric oxide in the skin, which widens blood vessels and may contribute to lower blood pressure.
However, experts stress that more sunlight does not mean more health benefits.
Daylight can affect sleep and mood
Natural light is an important signal for the body's internal clock.
Morning daylight helps the brain distinguish between day and night, supporting the sleep-wake cycle and helping people remain alert during the day.
Research has also linked greater exposure to daylight with aspects of cognitive performance and mental wellbeing. Insufficient exposure to natural light has been associated with sleep problems and low mood in some people.
So, how much sunlight is enough?
There is no universal number of minutes that applies to everyone.
The amount of exposure needed varies according to:
- Skin tone
- Age
- Location
- Season
- UV intensity
- Clothing
- Individual risk of skin cancer
Professor Mason said vitamin D production can be particularly efficient when UVB levels are higher, but exposure should remain brief rather than prolonged.
People with darker skin generally have more melanin, which provides some protection against UV radiation but can also mean vitamin D production takes longer.
Because UV intensity differs greatly between countries and seasons, experts caution against applying a single "safe" number of minutes to everyone.
Use the UV index as a guide
Experts say the clock alone is not a reliable way to judge whether sunlight is safe.
The UV index measures the strength of ultraviolet radiation reaching the Earth's surface. As the index rises, the risk of skin and eye damage increases.
People with very fair or sensitive skin, a family history of melanoma or skin cancer, numerous moles or weakened immune systems may need to take additional precautions.
When UV levels are high, experts recommend limiting unprotected exposure, covering exposed skin and using sunscreen.
Too much sunlight can be dangerous
The body does not continue producing unlimited amounts of vitamin D as sunlight exposure increases. However, the harmful effects of excessive UV exposure continue to accumulate.
Too much UV radiation can cause:
- Sunburn
- Premature skin ageing
- Pigmentation and other skin damage
- Eye damage
- Increased risk of skin cancer
UV exposure can also increase the risk of cataracts. Experts recommend UV-protective sunglasses when spending time outdoors in strong sunlight.
What about people who get too little sunlight?
Insufficient sunlight can contribute to vitamin D deficiency, particularly among people who spend most of their time indoors, live in regions with limited winter sunlight, have darker skin or keep most of their skin covered.
Severe and prolonged vitamin D deficiency can weaken bones and cause conditions such as rickets in children.
However, increasing UV exposure is not the only way to address vitamin D deficiency. Diet and supplements may also be appropriate, depending on individual circumstances.
Experts also caution against taking excessive amounts of vitamin D supplements, as very high doses can cause dangerously high calcium levels and damage the kidneys and other organs.
The right balance
Professor JoAnn Manson of Harvard Medical School advises against prolonged, unprotected exposure to sunlight.
The overall message from health experts is not to avoid daylight, but to find a balance between its benefits and the risks of UV radiation.
Regular outdoor daylight, appropriate sun protection and attention to the UV index can help people enjoy the benefits of natural light while reducing unnecessary exposure.
The key message: get daylight regularly, but avoid prolonged unprotected exposure and use the UV index—not the clock alone—to guide your time in the sun.
