How Does Sun Exposure Cause Premature Ageing?

Ageing is an inevitable process that occurs as a result of the normal and genetically determined breakdown of cells and tissues. This chronological ageing is also known as intrinsic ageing and simply occurs as we get older. However, there is a significant component of skin and overall cellular ageing that can be sped up or slowed down, and this is known as extrinsic ageing. This type of ageing can result in premature visible signs of ageing like fine lines, wrinkles, hyperpigmentation and textural changes and is impacted by environmental and lifestyle factors. In particular, exposure to ultraviolet (UV) light from the sun is a significant extrinsic contributor to ageing - known as photoaging.

What is Sun Exposure?

Sunlight is made up of three different types of UV radiation: UVA, UVB and UVC. UVC rays are mostly blocked by the earth’s ozone layer and so do not have a significant impact on our skin. UVB rays penetrate only to the outer epidermis skin layer and are responsible for sunburn. It also causes damage to the DNA in skin cells, contributing to skin cancer. 

UVA rays are less intense than UVB rays, however they penetrate deeper into the middle dermis layer of the skin. The dermis contains the skin proteins, collagen and elastin, as well as the blood vessels and nerve endings. Prolonged exposure to these UVA rays is responsible for the visible chronic skin damage that occurs as a result of photoaging. UVA rays are still very much present on overcast and cooler days and this is the reason why sunscreen should be worn everyday not just when the sun is out or the weather is warm.  

How Does Sun Exposure Cause Premature Ageing?

Interestingly, sun exposure is said to account for up to 90% of the visible signs of skin ageing and people with lighter skin (less of the pigment, melanin) are more prone to these visible changes. Sunlight damages the skin via a number of different mechanisms:

1. Oxidative Stress and Free Radical Production:

The ageing process is said to be at least partly due to damage arising from oxidative stress. Oxidative stress occurs as a result of the production of damaging molecules called free radicals or reactive oxygen species (ROS). These free radicals arise from different sources, however UV radiation from sunlight is a major source of free radical production. They damage the cells and tissues throughout the body and can cause the degradation of the collagen and elastin in our skin. Oxidative stress causes visible signs of premature aging like fine lines, wrinkles, hyperpigmentation, reduced skin moisture and skin sagging.

Antioxidants found in our body and in certain foods can help to neutralise these free radicals, and therefore minimise the damage to our cells and tissues. However, prolonged exposure to UV radiation and other free radical producers can overwhelm the antioxidant defences, leading to premature aging and overall tissue damage.

2. DNA Damage:

UV radiation exposure from sunlight causes mutations and damage to the DNA in our cells. Damage to the genetic material can occur due to both UVA and UVB radiation through the production of harmful free radicals and by causing errors in our DNA replication. As well as this, UV radiation can interfere with and inhibit the enzymes that are responsible for DNA repair as well as components of the immune system that act to remove mutated (cancerous) cells. Also, one study demonstrated that chronic exposure to sunlight shortens the telomeres of the epidermis. Telomeres are protective caps on the ends of human chromosomes. Damage to these telomeres can accelerate ageing and cause cancer development. These changes in combination not only cause significant visible damage but can lead to the production and acceleration of skin cancer cells.

3. Breakdown of Collagen and Elastin:

Collagen and elastin are the most abundant proteins in skin and help to provide structure, hydration and elasticity to the skin. The rate of production of these dermal skin proteins decreases as we age, causing the visible signs of aging like fine lines and wrinkles. However, in addition to decreased production, we can also influence the rate of collagen and elastin breakdown. Exposure to UV radiation from sunlight causes the production of the enzymes that breakdown collagen and elastin to be amplified. These enzymes are known as matrix metalloproteinases (MMPs) and include collagenases, metalloelastase and gelatinase.

Normally aged skin which has not been exposed to excessive amounts of sunlight, can be characterised by dryness, generalised wrinkling and a thinner appearance. However, studies have shown that photoaged skin has a leathery appearance with increased wrinkling, sagginess and fragility and impaired wound healing. These changes can also be observed on a histological (tissue) level under the microscope.

Is Sun Exposure Important?

Excessive and prolonged exposure to the sun can absolutely be damaging as established above. However, a small amount of regular and controlled exposure to the sun is vital for human health. The sun is our main source of vitamin D, an essential vitamin for the health of our bones, immune system, skin and overall well-being. Many studies have shown that deaths related to other cancers such as breast, lung and colon cancers, are lower in countries with warmer climates, showing a link between low vitamin D levels and certain cancers.

Exposure to sunlight, especially in the morning, is also vital for the production of our sleep hormone, melatonin. This exposure to morning sunlight has been shown to be effective against insomnia, seasonal affective disorder (SAD) and premenstrual syndrome. UV radiation from the sun also increases our blood levels of the body’s natural pain and stress relievers, endorphins. Sun exposure therefore positively impacts our mood, stress levels and sleep.

The recommendations on how much sun to get varies significantly and can be impacted by season, location, ethnicity, skin colour, etc. Regardless, even when out in the sun, it is important to implement protective measures to avoid the damage that can arise from sun exposure.

How do we Protect Ourselves from Photoaging?

To protect ourselves from the consequences and premature aging that can result from sun exposure, whilst also ensuring adequate sunlight for vitamin D production, we can implement certain measures:

1. Limit Sun Exposure:

Excessive and prolonged sun exposure can be damaging to our health as discussed. Whilst it is important to get some exposure to sunlight, it is wise to limit how much sun we are exposed to at any given time, especially during summertime and in hot climates. Some scientists recommend spending 3-15 minutes in the sun for people with fair skin and 15-30 minutes for individuals with darker skin tones. The exact amount of time varies depending on the time of day, climate and level of protection from other means. However, this recommendation is a guide to ensure adequate vitamin D production.

In order to avoid the potential consequences that can arise from insufficient vitamin D levels for individuals that get little to no sun exposure, many experts recommend ~4000 IU of vitamin D supplementation daily (however consult your doctor or health professional before commencing any supplementation).

2. Wear Sunscreen and Protective Clothing:

Sunscreen can protect us against skin cancer and the premature signs of aging that can result from sun exposure. SPF50+ broad spectrum, water resistant sunscreen is recommended regardless of weather and sun exposure level. All governing bodies also recommend that it is reapplied at least every two hours and after swimming or sweating. It is also said that some sunlight enters the skin even through a high-SPF sunscreen, so vitamin D can still be produced whilst wearing sun protection. We prefer a physical (mineral) sunscreen containing zinc oxide and/or titanium dioxide as they are a bit more effective than chemical sunscreens and tend to be more suited to people with sensitive skin. It is also important to wear sun-protective clothing when sun exposure is excessive. This can include long-sleeved clothing, wide-brimmed hats and sunglasses.

3. Use Antioxidant-Rich Skincare:

Topical application of certain antioxidant-rich skincare productions, for example, those containing vitamin A, vitamin C and vitamin E, can help to mitigate some of the photodamage that can result from excessive sun exposure. Of course, prevention is still far better than cure but this can be used as an additional aid against photoaging. One study found that topical vitamin C 5% cream that was applied to participants for six months led to visible clinical improvement in the appearance of photoaged skin.

4. Eat Sun Protective Foods:

Foods are not a replacement for the external sun protection strategies that we mentioned above, however, studies have shown that certain compounds found in foods can help to protect against photoaging. These compounds include carotenoids like lycopene and zeaxanthin, polyphenols like curcumin and resveratrol and antioxidant vitamins like vitamins A, C and E. For example, studies have shown that lycopene found in tomatoes can reduce sunburn caused by UV exposure. One study showed that participants consuming 40 g of tomato paste (containing ~16 mg/d of lycopene) over a ten week period had 40% lower sunburn rates compared with the control group.