Sun sensitivity, also known as photosensitivity, describes an abnormal or exaggerated reaction of the skin to sunlight, particularly its ultraviolet (UV) radiation components. This phenomenon manifests differently from a typical sunburn, presenting a range of symptoms that can include rashes, severe blistering, or other skin changes. Unlike a common sunburn, photosensitivity indicates a heightened vulnerability where even limited sun exposure can trigger a significant reaction. This increased sensitivity can stem from various internal and external factors.
How Skin Naturally Reacts to Sunlight
The skin naturally possesses mechanisms to interact with and protect itself from sunlight. Melanin, a pigment produced by skin cells, plays a central role in this protection by absorbing and scattering UV radiation. The amount and type of melanin determine an individual’s skin tone and their inherent ability to tan versus burn. Skin types are categorized by systems like the Fitzpatrick scale, which classifies skin based on its basal complexion, melanin level, and how it responds to UV exposure. Individuals with lighter skin, such as Fitzpatrick types I-III, have less melanin and are more susceptible to sunburn and DNA damage.
Sunlight contains different types of UV radiation, primarily UVA and UVB, which affect the skin in distinct ways. UVB rays penetrate the outermost layer of the skin, the epidermis, and are primarily responsible for sunburn and stimulating melanin production, leading to tanning. These rays are also directly absorbed by cellular DNA and contribute to skin damage and cancer risk. UVA rays penetrate deeper into the skin, reaching the dermis, where they contribute to collagen degradation and can also induce hyperpigmentation. Understanding these natural interactions provides a foundation for recognizing when the skin’s response becomes abnormally exaggerated.
Medications Causing Photosensitivity
Many medications can induce photosensitivity, broadly categorized into phototoxic and photoallergic reactions.
Phototoxic reactions are more common. They occur when a drug absorbs UV light, directly damaging skin cells. This results in an exaggerated sunburn-like appearance, with redness, swelling, or blistering, usually appearing within hours of sun exposure. Examples include certain antibiotics (tetracyclines, fluoroquinolones), NSAIDs (naproxen, ibuprofen), and diuretics (hydrochlorothiazide).
Photoallergic reactions are less common and involve an immune response. UV light modifies the drug, causing the immune system to recognize it as foreign. This triggers an allergic reaction, manifesting as an eczematous rash with redness, itching, or blisters, appearing one to three days after exposure. Unlike phototoxic reactions, these are not dose-dependent. Certain antifungals (voriconazole), tricyclic antidepressants, and retinoids (isotretinoin) can cause photoallergic reactions.
Underlying Medical Conditions
Lupus Erythematosus, especially systemic and cutaneous forms, often includes photosensitivity. UV light can damage skin cell DNA, leading to inflammation and characteristic rashes like the butterfly-shaped malar rash. Sun exposure can also worsen systemic symptoms such as joint pain or fatigue.
Polymorphous Light Eruption (PMLE) is a common rash from abnormal UV light reaction, often appearing in spring after initial sun exposure. It presents as itchy red bumps or blisters on sun-exposed skin, typically within hours. PMLE is a delayed hypersensitivity reaction, more common in women.
Porphyria is a group of genetic disorders where accumulated porphyrin precursors cause photosensitivity, particularly in cutaneous forms. Symptoms include painful blistering, skin fragility, and color changes on sun-exposed areas. Porphyria Cutanea Tarda (PCT) causes extreme sensitivity and blistering, while Erythropoietic Protoporphyria (EPP) causes immediate pain and burning.
Xeroderma Pigmentosum (XP) is a rare genetic disorder with severely decreased ability to repair UV-induced DNA damage. XP causes severe sunburn after minutes of sun exposure, premature skin aging, and a high risk of skin cancers, often by age 10.
Albinism, another genetic condition, involves reduced or absent melanin. This makes skin highly susceptible to sun damage and sunburn, increasing skin cancer risk due to lack of protective pigment.
Topical Products and Environmental Triggers
Certain topical products and environmental factors can heighten sun sensitivity. Perfumes and essential oils containing furocoumarins, like bergamot or lime, can induce photosensitivity when applied to skin followed by sun exposure, leading to discoloration or inflammation. Skincare ingredients such as alpha hydroxy acids (AHAs) and topical retinoids also increase skin’s UV vulnerability.
Phytophotodermatitis is a photosensitive reaction from contact with certain plants or their sap, followed by sun exposure. Plants with photosensitizing psoralens, such as celery, parsley, or figs, are common culprits. The reaction typically appears as linear streaks of redness, blistering, or hyperpigmentation on exposed skin, resembling a severe sunburn or chemical burn within 24 to 48 hours.