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Rashes to light | Photosensitivity, Photoallergic, Phototoxicity and Autoimmune

Updated: Jan 15, 2023

Photosensitive reactions can be either photoallergic or phototoxic... Read on...




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What is the difference between a photosensitive response and a phototoxic response? What is a photoallergic response?

Photosensitive reactions can be either photoallergic or phototoxic.

Photoallergic reactions occur when a skin rash develops from the combined effects of something ingested such as a medication, food, or vitamin PLUS light (mostly within the UVA, visible light range, or UVB range). These are often quoted as being "less common" than phototoxic reactions. However, I have to say that practically speaking in my outpatient suburban office setting I see these far more frequently than phototoxic ones. I suspect they may be underreported as they can be somewhat transient.



Where do photosensitive reactions typically appear?

The skin rashes that occur are on sun-exposed areas, including the face, neck, hands, and forearms. These rashes are itchy and inflamed. Often patients will describe them as tiny little sandpaper-like inflamed bumps that are exquisitely itchy. From experience I find that patients will often start with itchiness and then say to themselves "do I have a rash?"- then they may start asking others "do you see something on my skin- it’s so itchy!" The rash may show itself after the itching begins as inflamed patches or papules. It often looks like contact dermatitis. These reactions can take days to develop after exposure.

How do phototoxic reactions appear?

Phototoxic reactions look like a really bad sunburn. These also occur as a result of something ingested such as medications and develop within hours after exposure to the drug together with sunlight. UVA light is the most common trigger. These reactions can feel like sunburn- stinging/ burning sensations- and lead to blistering and peeling. Remember that SPF on products only tells us how much UVB is blocked by the product, not how much UVA is blocked. These reactions may appear in spite of using sunscreen products. Typically patients will think they are having a reaction to their sunscreen before thinking it may be related to some other trigger.

How are photosensitive reactions treated?

The treatment of photosensitive reactions is first identification and avoidance of the offending agent. Applying anti-inflammatory topicals, steroid topicals, and potentially oral steroids may be needed. Remember to use broad-spectrum sunblocks to prevent recurrences. If you must take a photosensitizing medication routinely, sun protective clothing is a better choice given the fact that UPF gives an indication of UVA and UVB blockage.

When should patients call or see their doctor about a sun-triggered rash?

This is where I think the photoallergic reactions are underreported. When someone experiences a phototoxic reaction it’s fairly obvious they need to seek help. There is significant discomfort. The offending drug may have been something recently started so it’s a bit more obvious to seek help to find an alternative medication to treat the underlying condition. To clear these rashes a course of oral steroids may be needed. Significant redness, swelling, blistering, chills, peeling, fevers, and fatigue- all are significant reasons to seek help.

For photoallergic reactions, I find that many times people have already managed these with topical cool compresses to relieve itching and assumed the sun played some kind of role based on the distribution of the rash. The main reason to seek care is if this is persistent or recurrent. You may need the help of your dermatologist to find the cause.

Do autoimmune diseases, such as rheumatoid arthritis, lead to photosensitivity?

Autoimmune conditions often have an independent risk of photosensitivity. And, yes, so do the medications used to treat these diseases. This is where taking the time to discuss the natural history, time of onset, and progress of the rash is important to review with your dermatologist.

What is your advice to patients with autoimmune illnesses who may be more sensitive to the sun?

It is important to understand that daily UV protection is essential, indoors and outdoors. Broad spectrum sunblocks, UV-protective clothing, hats, sunglasses- every step is helpful. The other thing to understand is that UV is not just outside. Some energy-efficient lightbulbs, gymnasium lighting, sunlight through the car window- UV is all around you and daily UV protection as a comprehensive approach will help prevent severed flares.


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