This is an important topic right now as we approach spring. The sun is getting stronger, the days are getting longer. It is very often at first exposure to sun in the spring, or when people go to the Caribbean for a sunny winter vacation.
The first category of dermatosis are UV induced rashes that are a result from an abnormal reaction to a normal exposure of UV light. Polymorphous Light Eruption (PMLE) is an example of a rash that is well known and very common. It is idiopathic, which means that it can come about spontaneously and the cause may never be known. It presumably can have a genetic component to it or be the result of an allergic response to the sun. The rash can present with a hive-like reaction or eczema-like blisters that starts after the first exposure to the spring sunlight and continues to harden over the course of the summer. It can occur within minutes of sun exposure or over a longer period of time of several days, and will resolve over the next week. It will be itchy. UVB light is implicated in 50% of the cases and UVA light in the other 50% of cases. If your physician is unsure about the cause, they can refer you for phototesting in your local Photobiology Unit. This is a painless procedure can use a positive photo test reaction to determine which spectrum of light is involved. Counterintuitively, some of these photodermatoses are then actually treated with photo-therapy treatment with either a narrowband UVB light or PUVA to harden the skin. Drugs can also be used such as Plaquenil ,a drug that is anti-inflammatory and is used in a variety the of photo sensitive disorders. In my experience, Plaquenil is a very safe, inexpensive and yet effective drug.
Yes, absolutely. Another example of an allergy to the sun is called Solar Urticaria. This is uncommon and occurs more rarely than PMLE. Hives usually begin with in minutes to less than 24 hours in sun exposed areas. Women are more commonly affected and very often starts in the fourth or fifth decade of life. It’s also symptomatic and very itchy. UVA light is implicated primarily in this type of reaction although UVB light and even visible light can be implicated as well.
There are common pre-existing skin conditions like eczema, psoriasis, rosacea or seborrheic dermatitis that are made worse by sun exposure. Again, counterintuitively, many of these patients will respond favourably with phototherapy where narrow bands of either UVB or UVA light used to treat the condition. It’s unclear why sunlight may make conditions like rosacea or psoriasis worse but are then treated with phototherapy. It could be that heat from the sun plays a role in exacerbating the condition. There are times where phototherapy will exacerbate the skin condition. In these instances, there could be an underlying systemic or auto-immune disease like Porphyria’s or Lupus erythematosus that are involved but potentially undiagnosed. These disorders can be ruled out with blood tests.
In all cases, it’s important to give your physician a full history of how and when the rash occurs, the associated symptoms, and existing conditions and disorders as these will all help with diagnosis. It’s always helpful to take pictures as well of the rash for a record. Sometimes, a physician will use these and the history for a diagnosis, especially for conditions like Polymorphous Light Eruptions. If they are unsure, they may use phototesting to confirm which part of sunlight could be the cause. They may then treat with either medication or photo-therapy and use blood tests to exclude other auto-immune diseases.
We know that UVA light can play a primary role in initiating many of these rashes. It’s important to protect your skin with a sunscreen with a high UVA Protection Factor of at least 10+ and then to apply sufficient quantities to get adequate broad-spectrum protection. We recommend using a sunscreen with a high concentration of zinc oxide, typically in the range of 20-25%. Sun protective clothing and hats are also incredibly useful, especially if you have pre-existing conditions like psoriasis, rosacea or a known auto-immune disorder like lupus.
Dr. Laughlin will continue with her discussion of rashes from the sun in our next blog to include drug-induced photosensitivity. We will also explore what the terms phototoxic or photo-allergenic mean and what the difference between the two are.
About the Author: Dr. Sharyn Laughlin, dermatologist, photo-biologist and luminary with over 40 years experience. In the field of cutaneous laser surgery, Dr. Laughlin is considered to be a leading expert by her peers in the medical community and the laser industry. Many of the new advances in cutaneous laser surgery and the pilot research for Health Canada or FDA approval took place at Laserderm under Dr. Laughlin’s experienced guidance. Dr. Laughlin has retired from her daily practice in Ottawa but continues to share her insight and expertise as a co-founder of The Sunscreen Company.
THE SUNSCREEN COMPANY TEAM MAY 16, 2022