Common hogweed (Heracleum sphondylium) often causes public concern because it shares a name with its notorious relative, Giant Hogweed (Heracleum mantegazzianum). Common Hogweed contains phototoxic compounds in its sap that can cause a skin reaction, but the danger is significantly less severe than that of the invasive species. The sap makes the skin hypersensitive to sunlight, potentially leading to blistering and burns. For most people, a reaction is mild, but understanding the difference between the two plants is important.
Identifying Common Hogweed and Giant Hogweed
The most significant difference between the two species is their sheer size. Common Hogweed typically reaches a height of 3 to 6 feet (1 to 2 meters) with a relatively thin, solid stem. Giant Hogweed, in contrast, is immense, growing up to 16 feet (5 meters) tall, with a thick, hollow stem that can be up to four inches in diameter.
Looking closely at the stems and leaves provides the most definitive identification points. Common Hogweed stems are green and covered in soft, white, downy hairs. Giant Hogweed stems are distinctly green with purple blotches, and covered in stiff, coarse bristles. The leaves of the common variety are generally smaller, up to 20 inches wide, and are broadly lobed with rounded edges. Giant Hogweed leaves are much larger, deeply divided, and have jagged, sharply pointed edges. The flower heads of Common Hogweed are smaller, usually flat-topped, and measure up to about 8 inches across, whereas Giant Hogweed produces massive, umbrella-shaped clusters up to 31 inches in diameter.
The Specific Mechanism of Skin Reaction
The skin reaction from both hogweed species is caused by a group of chemicals in the plant’s sap called furanocoumarins. These compounds are phototoxic, meaning they become highly reactive when exposed to ultraviolet A (UVA) light from the sun. When the sap contacts human skin and is then exposed to sunlight, the furanocoumarins absorb the UVA energy, which damages the skin’s cell structures, causing an inflammatory response and cell death.
The resulting condition is known as phytophotodermatitis, which manifests as a severe, delayed sunburn. Symptoms, including redness, a burning sensation, and blistering, typically emerge 24 to 48 hours after the initial exposure. While Common Hogweed sap contains these chemicals, its concentration is generally lower than in Giant Hogweed, meaning the resulting blisters are usually less severe. The area of contact can still result in long-term skin discoloration known as hyperpigmentation.
Immediate First Aid and Medical Attention
If the plant’s sap is suspected of having touched the skin, immediately and thoroughly wash the affected area with soap and cold water. After washing, the exposed skin must be covered immediately to prevent any further exposure to sunlight or other sources of UV light for at least 48 hours.
If a reaction develops, minor symptoms like redness and mild irritation may be managed with a cool compress or over-the-counter anti-inflammatory creams like hydrocortisone. Medical attention is necessary if large, painful blisters develop or if the rash covers a significant area of the body. Seek immediate medical help if the sap has contacted the eyes, as this can cause ocular burns and potentially lead to temporary or permanent vision impairment. Following a severe reaction, the affected area may remain sensitive for several months, requiring the consistent use of a high-factor sunscreen (SPF 30+) to prevent recurring burns or severe discoloration.
Safe Removal and Disposal Practices
When removing Common Hogweed from a garden or property, proper protective clothing must be worn to prevent sap contact. This includes long sleeves, long pants, waterproof gloves, and eye protection. The best time for removal is during the early spring before the plant has fully grown or produced its flower stalks. Cutting the plant’s taproot 6 to 8 inches below the soil surface with a sharp spade is an effective manual removal method for individual plants.
Using power tools like strimmers or weed whackers should be avoided, as they can aerosolize the sap and spray it onto the skin or into the eyes. If the plant is cut, care must be taken to prevent sap from spurting out of the cut stem. Unlike Giant Hogweed, which is classified as controlled waste requiring specialized disposal, Common Hogweed material can generally be bagged and disposed of with regular household waste. Ensure that all tools and contaminated clothing are thoroughly washed with soap and water after the work is completed to remove any lingering sap residue.