UV radiation and skin

Written by: Ana Vrbanović, MD

It is a well-known fact that ultra-violet sun radiation (UV radiation) is classified as cancerous due to its mutagenic properties and harmful effects which may lead to the development of skin tumours. On the other hand, human beings also need UV rays for vitamin D synthesis.

The skin is the largest organ in the human body and is made up of two parts: the epidermis and the dermis. The epidermis is the external layer which is in constant contact with external factors and has a huge role in defending the body from environmental stressors, various pathogens, chemical agents and UV radiation. The dermis is located beneath the epidermis and is made up of various tissue cells, skin adnexa, as well as immune system cells. Keratinocytes are the main, most numerous cells in the epidermis and due to their specific compounds they create a physical-chemical barrier amongst themselves. They retain melanin, but they are not responsible for its production. Melanocytes, the second most numerous cells in the skin are found in both the skin’s layers and are key in melanin synthesis. The function of melanin is to block UV rays from penetrating the skin. Secreted melanin is accumulated in keratinocytes in order to form a natural protective factor for the skin. Further, it is assumed that it also has other important roles such as protecting the skin against oxidative stress.

Skin can be classified using the Fitzpatrick scale, a semi-quantitative test consisting of comparing individual phenotypes, skin’s response to UV light and cancer risk (see link). According to the scale, each individual can be classified into one of the groups and taking into account the corresponding risk, care must be taken on proper protection and protective factor.

UV radiation contributes to skin inflammation, aging and the appearance of carcinoma. It is divided into three components: UV-A, UV-B and UV-C. Since ozone absorbs UV-C rays, when we talk about sun radiation we actually mean exposure to UV-A (90-95%) and UVB (5-10%) rays. UV-A penetrates deep into the dermis as opposed to UV-B which is almost completely absorbed by the epidermis. UV-A may create reactive oxygen compounds which may indirectly damage DNA. UV-B is directly absorbed by DNA which immediately leads to changes in molecular structure. Both modify DNA and may lead to malignant formations. As far as acute consequences of exposure to UV radiation are concerned, we may single out skin inflammation. UV-B prompts cascading of cytokines, vasoactive and neuroactive mediators that cause an inflammatory response of the skin and accompanying sunburn. If the exposure exceeds the inflammatory response limit this leads to shedding of keratinocytes i.e. shedding/flaking of skin. Exposure to UV rays leads to increase in the thickness of the epidermis, hyperkeratosis, which results in better protection of the skin from UV penetration. Apart from becoming thicker, in order to protect itself from UV radiation, the skin begins the process of melanisation or tanning.

Apart from the fact that free radicals, inflammations and constant DNA damage accelerate skin aging, the most dangerous consequence is the appearance of skin tumours. Skin tumours are one of the more common tumours in humans. It is supposed that UV radiation is the cause of 60% of melanoma and 90% of non-melanoma skin tumours. The most significant mechanism by which the damage occurs is by causing mutations on essential suppressor genes within the DNA, through direct and indirect influence of UV rays.

It is a common opinion that UV exposure should be avoided. The main related question that presents itself is how to compensate for the positive effects of UV rays – vitamin D synthesis. Even though Croatia is a Mediterranean country, its population still frequently lacks vitamin D. Its value can be checked at any family doctor’s office and if a deficiency is found, quality vitamin D supplements are easily obtainable.

Some of the most common recommendations for protection against UV exposure are:

  1. Reduce time spent outside during peak UV radiation hours (between 10 a.m. and 4 p.m.), seek shelter
  2. Avoid sun tanning which leads to sun burns (more than 5 burns increase the risk of skin cancer by double)
  3. Use protective factor 15 or higher on a daily basis, that protects both from UV-A and UV-B rays, and reapply multiple times during the day
  4. Use protective clothing, hats and UV-protective sun glasses
  5. Monitor the UV index and plan activities and UV radiation protection accordingly (http://www.epa.gov/sunwise/uvindex.html)
  6. Avoid artificial sources of radiation (tanning salons)
  7. Repair vitamin D deficiency by proper diet and supplements, after checking vitamin D levels at you family doctor’s office

Source: D’Orazio J, Jarrett S, Amaro-Ortiz A, Scott T. UV radiation and the skin. Int J Mol Sci. 2013;14(6):12222–12248. Published 2013 Jun 7. doi:10.3390/ijms140612222

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