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    Sun sensitivity caused by medication Recognising the symptoms and understanding the causes

    Many commonly used, even over-the-counter, medications can cause your skin to become more sensitive to the sun than usual. Photosensitising agents can become reactive or cause allergic reactions when they interact with ultraviolet (UV) light. This article details the causes, symptoms and management of drug-induced photosensitivity reactions.

    WHAT IS DRUG-INDUCED SUN SENSITIVITY?

    Woman taking medication
    Certain medications can increase the skin’s sensitivity to the sun.

    Drug-induced photosensitivity (or drug induced sun sensitivity) develops when a medicine, which does not normally cause sensitivity, undergoes photoactivation as it interacts with UV light when it enters the skin.

    Chemicals that have planar, tricyclic, or polycyclic structures absorb ultraviolet light, and often these altered chemicals cause cutaneous manifestations (such as phototoxic or photoallergic reactions). As stopping these medications is not always possible, it is important to understand how to protect skin from sunlight.

    WHAT ARE THE SYMPTOMS OF PHOTOSENSITIVE REACTIONS?

    The clinical features of drug-induced photosensitivity can vary, as the type of reaction, either phototoxic or photoallergic, depends on the type of photosensitising agent that caused the sensitivity reaction.

    Talk to your doctor or pharmacist if you’re worried about any of your symptoms, especially if you suspect you have drug-induced photosensitivity, or are not sure if your medication/s can cause photosensitivity reactions.

    WHAT IS THE DIFFERENCE BETWEEN PHOTOTOXIC AND PHOTOALLERGIC REACTIONS?

    The main difference is that photoallergic reactions occur when the immune system reacts to the photoactive chemical causing swelling and inflammation, while phototoxic reactions occur solely due to the photoactive chemical reacting directly with skin cell membranes and cellular DNA, and do not involve the immune system.

    Photoallergic reactions therefore only require a small amount of the photoactive chemical to be present as the immune system is very sensitive, while phototoxic reactions require a larger amount of the photoactive chemical to be present (although phototoxic chemicals differ in toxicity, and therefore different amounts of each chemical are required to cause a reaction).

    WHAT ARE THE VISUAL DIFFERENCES OF PHOTOTOXIC REACTION AND PHOTOALLERGIC REACTIONS?

    Close-up of skin with a photoallergic reaction
    Photoallergic reactions look more like Atopic Dermatitis.

    While phototoxic and photoallergic reactions are caused by different types of photoactive chemicals that induce different biochemical reactions, it can still be hard to differentiate between them when examining a person with photosensitivity. The main visual difference between the two reactions is that phototoxic reactions tend to look like severe sunburn that is mainly restricted to sun-exposed skin, while photoallergic reactions look more like Atopic Dermatitis and the reaction can spread from sun-exposed skin to unexposed areas.

    PHOTOTOXIC AND PHOTOALLERGIC REACTIONS – WHAT IS THE DIFFERENCE?

    Phototoxic Reaction

    Photoallergic Reaction

    Clinical characteristics
    Exaggerated sunburn

    Distribution
    Sun-exposed skin only

    Immunologically mediated
    No

    Incidence
    High

    More than one exposure to agent required
    No

    Quantity of agent required to induce photosensitivity
    Large

    Speed of reaction post exposure to photoactive agent and light
    Minutes to hours

    Clinical characteristics
    Dermatitis

    Distribution
    Mainly sun-exposed skin,  yet may spread to other areas that have not been exposed to the sun

    Immunologically mediated
    Yes; Type IV

    Incidence
    Low

    More than one exposure to agent required
    Yes

    Quantity of agent required to induce photosensitivity
    Small

    Speed of reaction post exposure to photoactive agent and light
    24-72 hours

    DEVELOPMENT (PATHOGENESIS) OF PHOTOTOXIC AND PHOTOALLERGIC REACTIONS

    What causes drug-induced photosensitivity reactions?

    Both systemic (oral) medications and topically applied compounds have the potential to cause photosensitivity reactions. It is therefore important to consider the possibility of photosensitivity when choosing a moisturiser or skin lotion. Some anti-inflammatory medications, or ‘painkillers’, such as ibuprofen can also cause photosensitivity. Other commonly used photoactive medications include antibiotics, non-steroidal anti-inflammatory drugs, diuretics, statins, retinoids and antifungals.

    Woman’s shoulder back
    Photosensitivity reactions may also result from topically applied compounds.

    What medications have the potential to cause photosensitivity?

    Many commonly used medications that can cause photosensitivity are included in the below table called Common Photosensitising Medications, however, this is not a complete list and there are many other medications that could potentially cause photosensitivity.

    Common Photosensitising Medications

    • Anticonvulsants (Neuroleptics)
    • Antibiotics
    • Diuretics
    • Hypoglycaemics
    • Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)
    • PDT Pro-Photosensitisers
    • Retinoids

    If you are not sure if the medication/s you are using can cause photosensitivity, or you want general information about which medications can cause photosensitivity, please ask your doctor or pharmacist.

    MANAGEMENT OF PHOTOSENSITIVE REACTIONS

    What is the best way to protect against photosensitivity, if you have to take a photoactive medication?

    Woman in hat
    A combination of proper clothing and a sunscreen with a high SPF is recommended.
    Woman applying sun screen her nose.
    Sunscreens are essential protection

    The wavelengths of light that are known to cause drug-induced photosensitivity reactions are UVA (320-400 nm) and UVB (290-320 nm) range. However, certain chemicals can react with sunlight in the visible range. Therefore, avoiding exposure to the sun is paramount.

    Furthermore, protecting skin by clothes and using a sunscreen with an effective UVA/UVB filter with a high SPF (50+) will help protect against the photoactivation of  most photoactive medication you may need to take. 

    Always follow the usage instructions on the sunscreen, especially with regards to frequency of application. Generally avoiding excessive exposure will also help to reduce the risk of drug-induced photosensitivity reactions. Read more about how to protect the face or on body.

    If you are at all concerned, always consult a doctor or pharmacist.