In the summer forest there are allergens and irritating substances that cause respiratory or cutaneous symptoms. Birch and alder pollen allergy is common in Finland. Pollens of other trees cause sensitization only sporadically. Spores of molds and mushrooms cause allergic reactions, but the means to study spore allergy are inadequate. Even edible mushrooms may cause allergic abdominal discomforts, and trehalose intolerance is supposed to be present in a small percentage of the population. Lichen allergens may bring about IgE-mediated reactions, contact allergy and photoallergic reactions.
There is more discussion and writing about the disadvantages of solar ultraviolet radiation than its benefits. Melanoma and other skin cancers have received most attention. Skin wrinkles and other signs of ageing or their prevention are being discussed. Instead only little attention has been paid on the anti-inflammatory properties and anticancer activity of UV radiation. Recent research has focused on sunscreen products, antioxidants preventing sunburn and its consequences, and urocanic acid, the skin's indigenous anti-inflammatory agent.