Introduction 

There are medications that, as a side effect, can cause skin sensitivity to sunlight, which is known as drug-induced photosensitivity. This article will discuss photosensitivity that is caused by medications. You may also hear photosensitivity referred to as “sun allergy” or photocontact dermatitis”.¹ 

Drug-induced photosensitivity can occur in anyone who takes medication that can cause sun sensitivity- of any age or sex. However, it is more common in those with lighter skin colours- this is especially true for those who burn rather than tan in the sun. Those with darker skin colours have more melanin, which protects the skin from UV damage. Still, those with darker skin should take precautions as this does not mean they will not acquire it.²

It is worth noting that photosensitivity is not the same as photophobia. Skin photosensitivity is when the skin has an adverse reaction to sunlight. Photophobia (literal fear of light) is when a person cannot tolerate the sight of light, but there are no adverse skin reactions. This may sound psychological, but it is often physically painful to look at light. Photophobia can occur in several conditions including, but not limited to migraines, schizophrenia, meningitis or certain eye conditions like dry eyes or conjunctivitis.³ 

What is photosensitivity?

As the name suggests, skin photosensitivity occurs when the skin has an adverse reaction to sunlight. There are two categories of drug-induced photosensitivity: phototoxicity and photoallergy. If photosensitivity is a common side effect, this will be noted in the information about the medication. Both types occur as a result of photosensitive drugs, plus exposure to UV rays. In rare cases, photosensitivity can be caused by light in the visible spectrum too.¹ 

Phototoxicity

Phototoxicity is the more commonly occurring type of sensitivity. UV rays damage the skin and generate small molecules called reactive oxygen species (ROS). ROS are free radicals, a type of charged atom or molecule, which can react with almost any other compound. When these ROS are in the skin, the body reacts to them.⁴

Phototoxicity usually results in a redness of the skin, known as erythema. There may also be swelling, itching or blistering of the area. The skin may be hot and painful. This is similar to a sunburn reaction and occurs within a few hours of exposure to UV light. After healing, it usually results in hyperpigmentation of the affected area.⁴ 

The usual course of treatment involves steroids, topically (like a cream applied to the area), or systemically (e.g. orally or IV). Antihistamines can also be given to relieve symptoms of itching and reduce swelling. Cooling the skin with cold water or an ice pack, and applying a soothing cream, can give immediate relief. Painkillers can be taken if required.⁴ 

Stopping the medication that is causing the photosensitivity would be one way to stop it from happening. But this is not always possible- the decision to stop has to be weighed up against the condition that is being treated. Sometimes altering the dose might be an option, this should of course be discussed with a doctor. Photosensitivity can persist for a period even after stopping the medication.^2,5,6,7    

Photoallergy 

Photoallergy is a much rarer type of photosensitivity. It is a delayed allergic response to a drug (an immune reaction), rather than because of cell damage in phototoxic reactions. Usually, the drug in photoallergic reactions is topical (applied to the surface of the skin, like a cream or gel) instead of systemic (e.g. taken orally). The light causes damage to the drug, and the body has a delayed allergic reaction to the products of that reaction (delayed meaning it occurs after a day or two following UV light exposure).⁴ 

The results of this are similar to a phototoxic reaction-redness of the skin, itching, and swelling. Treatment is also similar- stopping the drug if possible, and applying steroid creams, taking antihistamines to treat the site of the reaction. A photo patch test can be used to diagnose a photoallergic reaction. This is similar to a patch test for other allergens- several suspected allergens are applied to the skin, and then exposed to UV light. The one(s) that cause a photoallergic reaction can be determined after that.^2,5,6,7 

Drugs that cause photosensitivity

This is a non-exhaustive list, but the most common drugs causing photosensitivity are listed below:^2,6 

• Antimalarial drugs: Quinine and Hydroxychloroquine
• Tetracyclines, which are a group of antibiotics, are a common reason for photosensitivity 
• Biologic drugs, which are given for some autoimmune conditions, such as rheumatoid arthritis, lupus and psoriasis can also cause sun sensitivity. immunosuppressant, also given for these conditions that can cause photosensitivity 
• Tretinoin, used for acne
• Allopurinol, used for gout
• NSAIDs (non-steroidal anti-inflammatory drugs), such as Ibuprofen or Diclofenac. These may be taken orally, or used as a cream or gel
• ACE (angiotensin-converting enzyme) inhibitors are used for high blood pressure
• Diuretics are another type of drug, that can also cause photosensitivity 
• Chemotherapy drugs used for cancer
• Metformin, used for type 2 diabetes 
• Clopidogrel, an antiplatelet 
• Amiodarone, an antiarrhythmic drug (to regulate the heartbeat), used for atrial fibrillation
• Levothyroxine, a hormone replacement for underactive thyroid 
• Proton pump inhibitors (used for acid reflux) omeprazole and lansoprazole 
• Tricyclic antidepressants 
• Amlodipine and nortriptyline 
• Vitamin C 

Prevention 

The prevention of drug-induced photosensitivity and sun sensitivity is the same. To use SPF (sun protection factor) cream on exposed areas, reduce exposure to sunlight wherever possible. SPF creams should be of the highest possible factor ( usually factor 50), even if you are not going to spend 50 hours in the sun.⁶

Cover up as much as possible to minimise the amount of exposed skin, such as by wearing hats, sunglasses, long trousers and high-necked, long-sleeved shirts (the face and neck area are commonly affected by photosensitive reactions). In areas of intense sunlight, staying indoors when the sun is at its highest points (usually noon- early afternoon) is also advisable. UV rays are present during any daylight hours- regardless of whether or not it is sunny, so it is important to use sunscreen during all weather conditions. 

Other conditions 

Many other conditions can present with similar symptoms of redness, itchiness, blistering and pain in the skin which are not a result of drug-induced photosensitivity. These may be conditions that affect the skin directly, such as contact dermatitis from another allergen, like a cleaning product, but can also be systemic conditions which can have symptoms in the skin too, such as lupus or porphyria (although in these cases there will be other systems of the body affected too).^1,2,4 

Sunlight itself can cause skin sensitivity or sunburn. This can happen in anyone exposed to UV rays, but unlike with drug-induced photosensitivity, they do not need to take any drug that might cause the reaction. One type of photosensitive reaction is known as polymorphic light eruption (PMLE), where a red rash, which may be itchy, comes on the skin after exposure to sunlight. Again, this does not need any medication to occur. In addition to photosensitivity, UV rays are a cause of skin cancer. Increased photosensitivity can be a risk factor for skin cancer. Therefore,  the importance of covering up and using SPF in the sun is reiterated.^1,2,4,6 

Summary

Many medications have, as a side effect, sensitivity to sunlight. This is known as drug-induced photosensitivity. The most common drugs that cause photosensitivity are tetracycline antibiotics (like doxycycline), tretinoin for the skin, chemotherapy drugs for cancer and NSAIDs like ibuprofen. 

The main symptoms of photosensitivity are redness, swelling, itching and pain in the skin (similar to symptoms of sunburn). This will happen in the affected area of the skin that has been exposed to UV light. Treatment involves steroids (either topical or oral) and antihistamines. Stopping or changing the medication that is causing the photosensitivity may be an option for some cases. Other preventative measures are to cover up in the sun, and regularly use SPF cream on exposed areas.