Sunshine puts us in a good mood. This is true for most people. But some people suffer under the sun and its rays. Unfortunately, simply applying sunscreen is not enough for these people.

In our series on the interplay between people and the sun, we examine the reactions that light, especially UV light, triggers in the human body. We began by looking at IR radiation. In contrast to UV rays, which are not visible or directly perceptible, IR radiation is clearly noticeable. Our body absorbs its energy and the molecules start to dance around. The result of this is heat. Click here for the article on IR radiation.

When it comes to the reactions caused by UV radiation, photodermatoses, of which there are multiple variants, play a major role. Colloquially, these conditions are often grouped together and described as sun allergies. Strictly speaking, however, they are not allergies. Although, almost all of the disorders result from the direct influence of light and UV radiation on the body. If light and radiation are responsible for the health problems, they are also referred to as primary photodermatoses. In these cases, skin changes occur in the areas of the body exposed to the sun. 

Then there are secondary photodermatoses. Although light also plays a major role in these conditions, it is other internal causes that lead to the problems. Light and radiation act as a sort of trigger in these cases and affect the disorder. Genetic defects, metabolic disorders or autoimmune reactions are among the causes of secondary photodermatosis. A painful and dangerous interplay of factors. 

When the sun becomes your enemy 

Have you ever heard or read about xeroderma pigmentosum (XP) or erythropoietic protoporphyria (EPP)? Both are genetic and very rare disorders. In German, XP is often colloquially referred to as “moonlight disease”, and EPP is known colloquially as “shadow jumper disease”. Both disorders have one striking similarity, which is tragic for sufferers: they bring darkness into life.

A life in the dark 

Xeroderma pigmentosum (XP) becomes noticeable at a very young age. Photophobia can develop from around two years of age. Children instinctively try to protect their eyes from the sun. This strong photosensitivity may be an early indication of XP. It is followed by pathological skin changes. Brown spots can be seen on the face and the skin appears generally dry. Depending on the genetic variant, skin cancer often develops even before 20 years of age. Premature skin aging also increases. 

The cause of this disorder is a defective DNA repair system. Especially the areas of the body exposed to the sun are at risk of cancer. UV-B radiation in particular damages the skin. 

XP is not only rare, but also far from being fully researched. Despite being identified by Viennese dermatologist Moriz K. Kaposi in 1870, there is still no cure in sight. Sufferers must avoid UV light. Their light-sensitive skin must not get any radiation. Moonlight does not harm them, which is why they are commonly referred to in Germany as “moonshine children”.

However, it is important to note that tanning with afamelanotide is not to be confused with the use of self-tanners. These only color the skin and do not protect against UV radiation. Afamelanotide, however, is a synthetic form of a hormone that prompts skin cells in the body to make eumelanin. This increases tolerance to sunlight. 

Fortunately, for most people, sun protection is not as difficult as for patients with XP and EPP. A life filled with light is not only easier, but also much more pleasant. But it is still important to take sunscreen seriously and think about your health.