What is Photosensitivity from Food (Phytophotodermatitis)?
Phytophotodermatitis is a type of skin inflammation caused by contact with certain plants or food containing photosensitizing chemicals, followed by exposure to sunlight. The most common agents are a group of compounds called furocoumarins, particularly psoralens. When these chemicals are on the skin and react with UV-A light, they damage cells and trigger a toxic, sunburn-like reaction. This can result in redness, itching, and blisters, which can then lead to temporary or prolonged skin discoloration (hyperpigmentation). It's a non-immunologic reaction, meaning it can occur in anyone with sufficient exposure to both the chemical and UV light. The reaction is often delayed, appearing 12 to 72 hours after exposure.
The Role of Psoralens
Psoralens are natural pesticides that certain plants produce to protect themselves from insects and microbes. These small molecules can penetrate skin cells. When exposed to UVA light, they become activated and can cause cell damage or even bind to the DNA within the skin cells. High concentrations are most often found in the sap, rinds, or leaves of the plants, but can also be present in smaller amounts in the edible parts.
Common Foods That Increase Photosensitivity
Several everyday foods contain significant levels of photosensitizing compounds. Knowing which ones to be mindful of is the first step toward prevention.
- Citrus Fruits: Limes are the most notorious, leading to the condition known as "margarita burn" or "lime disease". Lemons, grapefruit, and bergamot oranges also contain furocoumarins that can cause a reaction. Contact with the juice, especially on a hot day, followed by sun exposure is a classic trigger.
- Celery: This vegetable contains psoralens and can cause phytophotodermatitis, particularly in those who handle it frequently, such as food workers. The risk increases if the celery is infected with fungus, which boosts the concentration of psoralens.
- Parsnips and Carrots: As members of the Apiaceae family (along with celery and parsley), these root vegetables also contain furocoumarins. Contact with the plant material is a more common cause of reaction than ingestion.
- Figs: The leaves and sap of the fig tree contain high levels of psoralens, which can cause severe phytophotodermatitis. While the fruit contains lower levels, contact with the milky sap is a significant risk factor.
- Herbs and Spices: Several common herbs and spices contain photosensitizing compounds, including parsley, dill, fennel, and coriander.
Other Sources of Photosensitizers
Beyond food, other substances and conditions can also increase your skin's photosensitivity. Certain medications, such as some antibiotics, diuretics, and NSAIDs, are well-known photosensitizers. Essential oils, especially those derived from citrus like bergamot, also contain high levels of phototoxic compounds. People with pre-existing conditions like lupus or eczema may also experience heightened photosensitivity.
A Comparison of Food-Induced vs. Drug-Induced Photosensitivity
| Feature | Food-Induced (Phytophotodermatitis) | Drug-Induced Photosensitivity (Phototoxicity) |
|---|---|---|
| Cause | Contact with photosensitizing plant compounds (e.g., furocoumarins/psoralens) and UV light. | Systemic medication or topical application of a chemical combined with UV light. |
| Incidence | Can occur in anyone; high exposure to UV and plant material is the main driver. | Varies depending on the drug; can affect a larger population if a commonly used medication is the cause. |
| Mechanism | Non-immunologic toxic reaction; the compounds directly damage skin cells. | Often a toxic reaction (phototoxicity) or an immune-mediated allergic reaction (photoallergy). |
| Appearance | Typically an exaggerated sunburn reaction, with redness, blisters, and streaky patterns where the substance touched the skin. | Looks like a severe sunburn (phototoxicity) or an itchy, eczematous rash (photoallergy). |
| Distribution | Restricted to areas of skin that had contact with the plant/food and UV light. | Restricted to sun-exposed areas for phototoxicity; may spread to unexposed areas with photoallergy. |
| Delay | 12 to 72 hours after exposure to both light and the substance. | Phototoxicity: minutes to hours. Photoallergy: 24 to 72 hours. |
Preventing Food-Related Photosensitivity
The key to preventing phytophotodermatitis is to limit the combination of contact with phototoxic foods and exposure to UV radiation. Here are some practical tips:
- Be Mindful of Handling: When preparing foods known to cause photosensitivity, especially fruits like limes and lemons, wear gloves. Wash your hands and any exposed skin thoroughly with soap and water after handling them and before going into the sun.
- Avoid Contact Outdoors: Be cautious when eating or drinking citrus-flavored beverages outside, especially on sunny days. If juice drips on your skin, wash it off immediately.
- Protective Clothing: If gardening or hiking in areas with wild plants like parsnips or hogweed, wear protective clothing, such as long sleeves and pants.
- Don't Rely on Sunscreen Alone: While crucial for general sun protection, sunscreen is not always effective against the specific reactions caused by furocoumarins. The best strategy is avoidance.
- Educate Yourself: Learn to identify wild plants known to be highly phototoxic, like giant hogweed, and avoid them.
Conclusion: Navigating Food and Sun Safely
While the concept that certain foods increase photosensitivity might be surprising, it's a well-documented phenomenon. The chemical reaction known as phytophotodermatitis is a direct result of photosensitizing compounds like psoralens, found in foods such as citrus fruits, celery, and figs, interacting with UV light. By understanding the common culprits and adopting preventative measures—like being cautious with food handling and washing exposed skin promptly—you can significantly reduce your risk of a painful, prolonged skin reaction. Remember, the goal isn't to avoid these nutritious foods entirely, but to be smart about how and when you interact with them, especially on sunny days. Being aware and proactive is the best way to enjoy both your meals and the sunshine safely. For more in-depth information on photosensitivity, visit Medscape's comprehensive article.
Common Phytophotodermatitis Trigger Foods
- Citrus Fruits: Limes, lemons, grapefruit, and bergamot oranges contain furocoumarins in their rinds and juice.
- Celery: Psoralens are present, especially in celery that is infected with fungus.
- Parsnips: The plant material and root contain photosensitizing furocoumarins.
- Figs: The milky sap from the leaves, branches, and fruit skin is highly phototoxic.
- Herbs: Parsley, dill, and fennel contain furocoumarins.
Actionable Prevention Steps
- Wash thoroughly: After handling citrus or other phototoxic foods, wash all skin that came into contact with them.
- Use gloves: Wear gloves when preparing or harvesting produce known to contain high levels of photosensitizers.
- Be aware of wild plants: Know how to identify and avoid wild parsnip and giant hogweed, which are highly phototoxic.
- Avoid outdoor handling: Don't squeeze limes or lemons for drinks while sitting in the sun.
- Recognize symptoms: Be aware of signs like redness, itching, and blisters appearing 1-3 days after sun exposure and contact with a trigger.
