Sunlight is the source of the growth of all things. Sunlight can increase the resistance of the skin. No wonder many people like to expose themselves and receive the caress of the sun. But when swimming by the water in summer, playing or working in the hot sun, have you ever imagined that the sun can also cause skin diseases.
Phototoxic dermatitis is caused by a phototoxic reaction, not an allergic reaction, it can happen to most people, and it will get sick the first time it is exposed. Generally speaking, acute phototoxic reactions are characterized by erythema, edema, and sometimes blisters, which then subside leaving pigmentation and desquamation. The reaction is confined to the exposed area, starting from a few minutes to a few hours after the sun, and reaching its peak in a few hours to a few days. The patient may feel burning pain, typically like the sunburn common in summer. Chronic reactions are visible changes that occur to the naked eye after repeated exposure to sunlight for several years, including wrinkles, atrophy, hyperpigmentation and hypopigmented spots that make people look old. In addition, there will be telangiectasias, yellow papules and plaques, and skin cancer. Chronically damaged skin is very fragile and can rupture after minor trauma, forming star-shaped scars later, and the blood vessels in the skin are also prone to rupture leading to purple spots.
Photoallergic dermatitis This type of dermatitis is caused by light waves with a spectral wavelength of 320 to 425 mm. It is an allergic reaction and only occurs in a small number of people with specific allergic constitutions. It takes about 5 to 20 days for the patient to develop the disease after being exposed to the above light for the first time. If the photosensitive substance is repeatedly used in the future, even if the amount is very small, the exposure is very small, and the disease can still occur within 24 hours. The rash is like allergic contact dermatitis, with erythema, papules, blisters, erosions, and exudate with clear boundaries. Except for exposed parts, the severe ones can be extended to other parts of the body.
In addition, there are some special performances, such as——
Solar urticaria manifests itself as itching after a few minutes in the sun, followed by erythema, followed by a blushing wind mass, which usually subsides within 1 to 4 hours.
Polymorphic light eruption is a few hours to 4 days after light exposure, and local pleomorphic rashes, such as papules, blisters, nodules, plaques, and even eczema and extensive erythema, exist at the same time.
The photoallergic reaction of exogenous chemicals generally involves repeated exposure to photosensitive chemicals (such as cosmetics, chemical aerosols), and then the above-mentioned rashes from pimples to eczema occur slowly.
Why does sunlight (including some artificial light sources) cause skin diseases? In fact, the pathogenesis of light-sensitive skin diseases is more complicated. Generally speaking, light irradiation works by exciting molecules. When a molecule absorbs light of a specific wavelength, it is excited to emit heat and fluorescence, or remains in an excited state and reacts with neighboring molecules to release energy , Causing harmful biological reactions. There are some molecules in the skin that can be excited by light energy, such as proteins, nucleic acids, sterols and other molecules with ring structures and double bonds. Therefore, swimming, sunbathing, traveling and field work should be properly shaded and not wanton exposure to the sun to avoid skin damage. It is true that light-sensitive skin diseases are rare after all. Because the skin itself has a good protective effect on light, such as stratum corneum, sebum, sweat, etc. can absorb or reflect a certain amount of light, especially melanin, which can absorb more ultraviolet rays without being stimulated to cause adverse reactions and protect the human body Protect from light damage. Because of this, people of color suffer less from skin cancer than whites when they are also exposed to sunlight.
Various light-sensitive skin diseases should be treated appropriately according to the situation, and it is best to consult a dermatologist. Generally, antimalarial drugs such as chloroquine are effective for photoallergic dermatitis; corticosteroids have a control effect on acute inflammation; antihistamine drugs can inhibit the acute response caused by photoallergic. 3% boric acid water can be used locally as a cold wet compress, or externally applied hormone ointment such as skin relief. It is best for people who have been sick to stop using or isolate them after discovering the light-sensing substances that cause illness. Avoiding the sun and other light is the best choice.