Wild parsnip (Pastinaca sativa) is a common plant found along roadsides and in open fields. Contact with its sap can cause a painful, burn-like skin reaction. This reaction is not an allergic response but a severe rash that occurs when the plant’s chemical compounds are activated by sunlight. If you or someone you know has come into contact with this plant, understanding the specific nature of the rash and knowing the proper steps for treatment is important.
Understanding the Reaction
The severe rash caused by wild parsnip is medically termed phytophotodermatitis, meaning skin inflammation induced by a plant and light. The plant’s sap, found in the leaves, stems, and fruits, contains chemicals called furocoumarins (psoralens). These compounds are phototoxic, becoming highly reactive when exposed to ultraviolet (UV) light, even on cloudy days. The rash only develops if the skin exposed to the sap is subsequently exposed to the sun.
Once activated by UVA light, furocoumarins penetrate skin cells and cause damage similar to a chemical burn. This results in a painful, blistering rash that typically appears 24 to 48 hours after sun exposure. This is a direct, toxic reaction, unlike an allergic reaction like poison ivy. The severity depends on the concentration of sap on the skin, the duration of sun exposure, and individual skin sensitivity.
Immediate Treatment and Symptom Management
The single most effective action immediately following potential exposure is to shield the affected area from all sunlight and thoroughly wash the skin. Furocoumarins must be removed before UV light activates them, so cover the exposed skin and move indoors quickly. Once inside, wash the entire area with mild soap and warm water for at least ten minutes. Any clothing that may have sap on it should also be washed immediately to prevent further contamination.
If symptoms, such as redness, burning, and blistering, have already appeared, treatment shifts to managing discomfort. Applying cool, damp compresses or taking an oatmeal bath can help soothe the intense local burning and itching. Over-the-counter anti-inflammatory medications like ibuprofen can be used to manage pain. For localized itching, a low-potency hydrocortisone cream may provide relief, though severe inflammation may require prescription-strength topical steroids.
Small blisters should be left intact, as the skin acts as a protective, sterile barrier against infection. If a blister is large or ruptures, the remaining skin flap should be left in place and the area gently cleaned. For weeping blisters, a cool compress soaked in an astringent solution, such as Burow’s solution, can help dry the area. Applying an antibiotic ointment to broken skin and covering it with a non-stick bandage will help prevent secondary bacterial infections.
When to Seek Medical Attention
Seek professional medical attention if the rash covers a large percentage of the body or if blisters are extensive and severe. A doctor’s visit is necessary if the rash involves sensitive areas like the eyes or face. You should also seek care if you notice signs of infection. Signs of infection include increasing pain, swelling, warmth, pus, or a fever.
Preventing Future Exposure
Avoiding contact with wild parsnip begins with proper identification of the plant. It can grow up to five feet tall and is characterized by its hollow, grooved stem. The plant produces umbrella-shaped clusters of tiny, bright yellow flowers, typically blooming from May through August. Its location along trails, roadsides, and in open, sunny disturbed areas makes it a frequent hazard.
When working in areas where the plant is known to grow, wear protective clothing, including long sleeves, long pants, and gloves. Protective eyewear is also a prudent measure, as sap can splash and spray, causing injury to the eyes. After any outdoor activity in infested areas, thoroughly wash all tools, equipment, and clothing to eliminate any residual sap.
A significant long-term consequence of the rash is post-inflammatory hyperpigmentation, appearing as a dark brown discoloration where the burn occurred. This darkening is caused by the melanocytes in the skin producing extra pigment in response to the initial severe inflammation. To minimize this effect, strict sun avoidance of the affected area is necessary for months, as UV exposure will cause the dark spots to intensify. While this discoloration can persist for up to two years, dermatological treatments may accelerate fading.