Special Feature on Sun Protection

Protecting ourselves from the sun, by Mercedes Camps Miró.

The influence of the sun on life on the surface of our planet is undeniable. Its effects on biology are clear and varied, and it is absolutely essential for the sustainability of terrestrial ecosystems. We humans, as inhabitants of this world, are exposed to its influence and the effects of its radiation, and we derive clear health benefits from this.

However, this exposure is not without risks, and there is a clearly defined range of problems and illnesses that result directly from exposure to the sun. To avoid these harmful effects, we must adopt behaviours that prevent prolonged exposure to the sun or use protective measures to safeguard ourselves when we are going to be exposed.

Solar radiation

Let’s now take a look at the radiation spectrum which reaches the Earth’s surface:
The ultraviolet (UV) radiation covers the range between 100 and 400 nm, the visible light covers the range between 400 and 760 nm (violet, blue, green, yellow, orange, red), the infrared radiation ranges from 760 nm to 4000 nm. The latter is responsible for the heat input into our environment.

We shall spend a little more time describing ultraviolet radiation, as it is responsible for the main biological effects that we shall describe later. Ultraviolet radiation can be divided into different types or spectral ranges:

• Ultraviolet C or UVC, which range from 100 to 290 nm, do not reach the Earth’s surface as they are absorbed by the ozone layer. They have germicidal properties and are erythematogenic and mutagenic. They are used to sterilise the air in rooms. People who are exposed to this radiation should wear protective eyewear to avoid the risk of conjunctivitis and corneal irritation.
• Ultraviolet B or UVB, which ranges from 290 to 320 nm, is the radiation responsible for sunburn and skin cancer; it also causes irritation to the conjunctiva and cornea and is responsible for the actual tanning process.
• Ultraviolet A or UVA, the range between 320 and 400 nm can in turn be divided into two bands: UVA I (340–400 nm) and UVA II (320–340 nm). UVA rays are responsible for immediate tanning and photoageing; the UVA II band has the greatest tanning effect and is also the most erythematogenic.

There are others factors affecting UV radiation which reaches the earth as:

• Atmospheric Ozone
• Solar lift
• Altitude
• Atmospheric dispersion
• Clouds and Dust

The skin: How does solar radiation affect it?

The skin It is one of our largest organs, with a surface area of 1.8 m², and our primary protection against the external environment. Its main functions are: the protection against external threats, opposite the solar radiation, functions metabolic, thermoregulatory, immunological and relationship with the external environment thanks to his sensitivity.

Let’s go over the the structure and functions of the skin.

The skin consists of three layers: the epidermis, the dermis and the hypodermis.

• The epidermis It originates in a basal germinative layer composed of keratinocytes, which, as they divide, give rise to the upper layers. As the keratinocytes move towards the surface, they age and gradually change in appearance whilst undergoing metabolic changes, accumulating the protein keratin, becoming dehydrated and giving rise to the spinous and granular layers. Finally, the keratinocytes lose their nucleus, flatten completely and come to be known as corneocytes, forming the superficial stratum corneum which is continuously shed in the form of flakes. In addition to keratinocytes and corneocytes, the epidermis contains melanocytes and Langerhans cells; both types of cell have a dendritic appearance. Melanocytes are the cells that synthesise melanin, which is subsequently transported to neighbouring keratinocytes. Langerhans cells play an important role in immune defence. Burns that damage only this layer are classified as first-degree burns.

• Located beneath the epidermis, the dermis It is made up of fibroblasts that synthesise the extracellular connective tissue. This tissue consists essentially of a gel of glycosaminoglycans and proteins. Collagen is the main structural protein of the dermis, whilst elastin forms a network of interconnected fibres that provides the skin with elasticity and flexibility. Glycosaminoglycans are macromolecules with important moisturising functions. The connective tissue contains the sebaceous and sweat glands, hair follicles, nerve endings, lymph nodes, and a network of capillaries that supply nutrients to the epidermis. Langerhans cells can also be found in the dermis. If the burn reaches this layer, it is a second-degree burn.

• The hypodermis It is the deepest layer, connecting the skin to the muscle tissues. It consists mainly of connective and adipose tissue, and provides thermal insulation and mechanical protection; when a burn reaches and penetrates this layer, it is classified as a third-degree burn – the most severe type – and is likely to leave scars.

The skin’s defence mechanisms

It is obvious that we are constantly exposed to the sun, so our skin has a number of defence mechanism against the harmful effects of UV radiation. These mechanisms have enzymatic and non-enzymatic components. Among the former are the leading antioxidant enzymes: superoxide dismutase, catalase, thioredoxin reductase, and glutathione peroxidase and reductase; the role of all these enzymes is to eliminate free radicals produced by both radiation and cellular metabolism.

The non-enzymatic components It consists of a series of molecules with antioxidant activity; these react with free radicals, halting the oxidative chain reaction. It is mainly composed of vitamin C (ascorbic acid), the vitamin E (α-tocopherol), beta-carotene y ubiquinone (coenzyme Q), and the lipoic acid found in the mitochondria.

Other ccompounds with antioxidant properties are: the vVitamin A, carotenoids (beta-carotene, lycopene and lutein), trace elements (Se, Cu, Mn), polyphenols (anthocyanins, xanthines, flavonoids), omega-3 fatty acids (eicosapentaenoic acid, fish oil, borage oil) and various extracts (polypodium, pycnogenol, tea).

The beneficial and harmful effects of UV radiation

The beneficial effects of UV radiation

We are drawn to the sun, and that makes sense. Solar radiation is largely healthy; it gives us a sense of optimism and has a number of beneficial effects on our bodies. This sense of optimism is thought to be due to the effects of light on melatonin, a thermal effect caused by infrared radiation, whilst conditions such as acne and psoriasis improve thanks to UV radiation. The main benefits of exposing the skin to UV radiation are: the synthesis of vitamin D and melanogenesis.

Harmful effects of UV radiation

Sun exposure is not without risks; depending on our skin type and our work and leisure habits, we are at varying risks of developing skin problems caused by UV radiation. Depending on how the skin reacts to solar radiation, it has been classified into six types. These types take into account the erythematous reaction (or sunburn) and the propensity to develop photoageing, based on skin colour and tanning ability.

Skin types and their characteristics

Classifying people’s skin into phototypes is extremely helpful for professionals, as it enables them to estimate the relative risk the risk a patient has of developing acute and chronic conditions as a result of exposure to UV radiation.

The main problems we may encounter when we are exposed to solar radiation without adequate protection are essentially: the sunburn o burnthe photoageing o dermatoheliosis and the skin cancer as the most important ones.

We can distinguish between, according to the Fitzpatrick scale, among the following skin types: 

• Skin type I, have pale white skin, blonde hair, blue or hazel eyes, with or without freckles (ephelides). They are very sensitive to UV radiation, burn easily and find it difficult to tan; they suffer from severe and premature photoageing and are at high risk of developing skin cancer.
• Skin type II, have fair skin, very similar to the previous type, with very fair or blond hair, but are more resistant to sunburn; they do tan slightly and are also prone to premature photoageing and are at high risk of developing skin cancer. This type and the previous one are considered to have compromised melanocytes.
• Skin type III, They also have fair skin, are resistant to sunburn and tan moderately; they experience intense but not premature photoageing, and their risk of developing skin cancer is moderate.
• Skin type IV, Their skin is tanned in colour, with slight pigmentation; they are moderately sensitive to UV radiation. Like the previous type, they are melanocyte-competent, and their ability to tan provides them with some protection against the effects of sun exposure. They burn very little, their risk of developing skin cancer is low, and photoageing is moderate.
• Skin type V, with dark skin, they rarely get sunburnt and develop a dark brown tan; their risk of skin cancer is minimal, and the photoageing they experience is slow and does not become apparent until they are in their 40s or 50s.
• Skin type VI, dark brown or black skin; they never get sunburnt and their risk of skin cancer is virtually zero; photoageing is slow, occurs later in life and is minimal.

Sun protection or photoprotection

To avoid the harmful effects of solar radiation, and in particular those resulting from exposure to UV radiation, we can turn to the use of clothing, hats, sunglasses and avoid exposure to the sun during the middle of the daya.

When this is not possible due to the nature of the activity we are engaged in – be it work, sport or outdoor leisure – we will have to resort to using protectores solares appropriate measures to protect ourselves, particularly from the effects of UV rays.

As part of the strategy of a sun protection We have a number of resources at our disposal, and we must use them in accordance with the weather conditions and in line with our skin type skin. In other words, we need to have the right information and advice. We must therefore be familiar with both the types of protectors available such as the UV radiation intensity that we’re going to come across out there.

Sun Protection Factor (SPF)

To ensure that choosing a sun protection product We will take into account a figure that is clearly highlighted on its labelling and product information; this is the Sun Protection Factor (SPF). This factor tells us the level of protection the product offers and gives us an idea of how long we can spend in the sun after applying it without getting sunburnt. Let’s say that The higher the SPF, the longer we can stay in the sun without getting burnt.

The UVI index

How much UV radiation reaches the Earth’s surface? This would be the other key factor in determining what we need to do to protect ourselves properly from the effects of UV radiation.

The amount of UV radiation to which we are exposed depends on the seasonthe solar timethe latitude in which we live and of the altitude relative to sea level, wherever we are.

To find out this information, the UV Index, based on an initiative jointly promoted by the World Health Organisation (WHO), the World Meteorological Organisation (WMO), the United Nations Environment Programme (UNEP) and the International Commission on Protection against Non-Ionising Radiation (ICPNIR), with the aim of formulating some recommendations on how to calculate, express and disseminate the use of a global solar UV index.