In summer, or even in spring, they consult us about “sun allergy” symptoms. In general, these are patients who, after being exposed to the sun for a couple of hours, have presented itchy skin and skin lesions that they describe as “rash or rash”.
Can the sun cause “allergy”?
Ultraviolet radiation from sunlight is one of the main environmental factors affecting human health. The most frequent reactions produced by sun exposure are sunburn and tanning. If exposure is repeated, chronic skin changes occur that can trigger cancer and photoaging. But solar radiation can also alter the immune system leading to an abnormal skin reaction after sun exposure. These abnormal reactions are known as “photodermatosis” and usually include those skin lesions that patients known as sun allergy.
What is photodermatosis?
As mentioned before, photodermatosis is an abnormal skin response caused, triggered or aggravated by exposure to radiation emitted by the sun. The clinical manifestations are very varied and range from itching, to skin lesions such as hives, exanthema (redness), eczema or even scabs.
Which are the most frequent photodermatoses?
The most frequent photodermatoses secondary to the interaction between solar radiation and the immune system are polymorphic light eruption, solar urticaria and chronic actinic dermatitis. Each of these manifests itself in a different way, but in some cases, especially those with many years of evolution, the skin lesions can overlap, generating confusion when establishing the diagnosis. It is important to remember that solar radiation can also worsen atopic dermatitis.
What is the Polymorphic Light Eruption?
It is the most common photodermatosis in our setting, being the adult population the most affected. Young women, especially those between the second and third decades of life, are the ones who present the most.
Polymorphic light eruption is the skin reaction that most patients describe as “sun allergy”. This is because symptoms can occur within a few hours of receiving sunlight and usually start with itchy skin that is then accompanied by papules, vesicles, eczema, plaques, erosions and scabs. It is because of these different forms of skin lesions that it is called “polymorphic eruption”. The face, neck, upper thorax, forearms and legs may be affected.
The main cause is sun exposure, it usually appears at the end of spring and improves as the summer progresses. This improvement is due to the fact that repeated exposure to the sun facilitates a phenomenon called “hardening”. This phenomenon is a process of photoadaptation that the skin develops as sun exposure increases progressively, creating “resistance” or solar tolerance.
What is Solar Urticaria?
As in polymorphic light eruption, it is a common photodermatosis in young adults (especially between 20 and 30 years of age) and in females. Despite its “popularity” among reactions due to the sun, solar urticaria is a rare condition. It only represents 0.4% of all cases of urticaria.
Solar urticaria is characterized by skin itching accompanied by habonous lesions (wheals/hives). Syntomas usually starts very quickly after sun exposure. At first it is only itching and erythema (redness), but as time progresses, hives appear. The condition usually resolves spontaneously within 24 hours, without scarring.
The most affected sites are those known as “photoexposed areas” which include neck, arms and forearms. As also happens with polymorphic light eruption, in solar urticaria, repeated exposure to the sun facilitates the “hardening” of the skin, which is why the face and the back of the hands may not present lesions despite being areas more commonly exposed to sunlight. When large areas of the body are affected, the skin condition may be accompanied by headache, malaise, nausea, and cardiovascular symptoms, such as tachycardia, hypotension, and even shock.
What is Chronic Actinic Dermatitis?
It is the photodermatosis with the largest worldwide distribution, being more frequent in temperate regions and in men over 50 years. They are usually patients with a history of significant sun exposure.
Lesions appear on exposed skin areas with sharply separating cut lines where clothing protection begins. They are patchy lesions that appear in the form of eczema. In severe cases, lesions may become lichenified. When the condition is very intense, it can affect the palms and soles, there are even patients who can lose the hair of the eyelashes, eyebrows and scalp, generally secondary to scratching.
It is common to worsen in the summer, developing lesions within minutes or hours after exposure to the sun which, occasionally, may recur after several days, if exposure stops and the reaction is mild. In severe forms the patient may have lesions throughout the year.
How can photodermatoses be prevented?
The best prevention is adequate photoprotection. For this we must avoid direct sun exposure, wear clothing that covers the most photoexposed areas and apply sunscreens (UVA and UVB).
Is there a specific treatment for photodermatoses?
Currently there are many treatments for the control of photodermatoses. These range from antihistamines, corticosteroids, immunosuppressants and even ultraviolet radiation. Treatment must be individualized since, as we saw earlier, the clinical manifestations are diverse and can occur at different stages of the disease.
At ClinicAL we hope to have provided information on the most frequent skin reactions caused by sun exposure, which are so frequent in these months.