Sun and UV rays

Positives and negative effects

The sun provides many positive effects for each of us. The general well-being is increased, immune defences are strengthened, blood pressure and cholesterol levels are lowered and blood circulation and metabolism are stimulated. The body needs a minimum amount of sunlight in order to produce vitamin D, which the body needs for an intact calcium balance.

However, excessive sun exposure can have negative effects on the body. Acute sun damages can occur immediately, after hours or days. Sunburn, sun allergies (light dermatosis), other phototoxic reactions, but also sunstroke and head stroke can occur. Fortunately, for some time now people have also become more and more aware of chronic sun damages. The danger to suffer from black or white skin cancer, but also the accelerated skin aging or the formation of pigment spots caused by excessive exposure to the sun, is meanwhile know by broad public.

Repeated sunburns in childhood are the main reason for chronic sun damages!

Sunlight spectrum of the sun and its effects on the skin

Sun rays are electromagnetic waves with different wavelengths. From the solar spectrum shown above, only UVA and UVB rays, visible light and infrared rays reach the earth’s surface. Even if UV rays only make up 4.3% of the total solar spectrum, they have a great impact on the skin. UV rays differ regarding:

  • Their biological effects on the skin
  • The depth to which they penetrate the skin
  • Their energy
UVB radiation The short-wave UV-B rays are absorbed to 90% by the ozone layer. The intensity of transmitted rays varies and depends on a number of factors (see sun protection). UVB rays are largely absorbed by the upper layers of the epidermis and reach only a very small proportion of the basal cell layer (see figure below). UVB rays cause a tanned complexion and the thickening of the horny layer (formation of the so-called light callosity), stimulation of the melanin formation and support of the vitamin D synthesis. Nevertheless, UVB rays are mainly responsible for sunburn, allergic reactions and damages to nucleus. By summing up these nuclear damages, the disposition for the formation of skin cancer is created.
UVA radiation

UVA rays penetrate into the dermis with the connective tissue and blood vessels. There they act on the tear-resistant collagen fibres and elastic fibres. The latter are responsible for the suppleness and adaptability of the skin. If excessive exposure to UV-A radiation occurs, the resilience of the elastic fibres is impaired and the connective tissue weakened. The consequence: The skin ages faster, becomes limp and wrinkled.

It is also proven that UVA rays are responsible for the formation of free radicals, which increase the risk of certain types of skin cancer.

Additionally, UV radiation is responsible for the development of pigment disorders, the increase in light sensitivity after taking certain drugs, as well as polymorphic light dermatosis, commonly known as “sun allergy” or “Mallorca acne”.

Image of the penetration of UV rays into the skin