Phototoxicity

Phototoxicity

Phototoxic reaction on skin after exposure to Rue officinale.

Phototoxicity is a chemically induced skin irritation that requires light exposure to activate the chemical agent. This condition is often confused with photoallergy, but unlike photoallergy, phototoxicity does not involve the immune system. Instead, it is a non-immunologic response that occurs when a phototoxic agent absorbs ultraviolet (UV) light and releases energy that damages surrounding tissues.

Mechanism of Action

Phototoxic reactions occur when a phototoxic substance absorbs ultraviolet radiation and becomes excited to a higher energy state. This energy is then transferred to surrounding molecules, leading to the formation of reactive oxygen species (ROS) and free radicals. These reactive species can cause direct damage to cellular membranes, proteins, and DNA, resulting in inflammation and cell death.

Common Phototoxic Agents

Phototoxicity can be triggered by a variety of substances, including certain medications, cosmetics, and plants. Some well-known phototoxic agents include:

• Psoralens - Found in plants like Rue officinale and used in PUVA therapy for psoriasis.
• Tetracyclines - A class of antibiotics that can cause phototoxic reactions when patients are exposed to sunlight.
• Fluoroquinolones - Another class of antibiotics known for their potential to cause phototoxicity.
• Coal tar - Used in the treatment of skin disorders, it can cause phototoxic reactions when exposed to UV light.

Symptoms

The symptoms of phototoxicity are similar to those of a severe sunburn and can include:

• Redness and inflammation of the skin
• Blistering
• Pain and tenderness
• Swelling

These symptoms typically appear within minutes to hours after exposure to the phototoxic agent and sunlight.

Prevention and Management

Preventing phototoxicity involves avoiding exposure to known phototoxic agents and minimizing sun exposure, especially during peak UV radiation hours. Protective clothing and broad-spectrum sunscreen can also help reduce the risk of phototoxic reactions.

Management of phototoxicity focuses on symptomatic relief and may include:

• Cool compresses to soothe the skin
• Topical corticosteroids to reduce inflammation
• Analgesics for pain relief

Related Pages

• Photoallergy
• Sunburn
• Psoriasis
• PUVA therapy