Giant Hogweed represents a potentially very serious human health risk and you might be breaking the law by not controlling it. Add to that the potential for a mature plant to dump fifty thousand seeds on your land and the considerable difference in the effort, risk and cost between treating one or two immature plants and it’s clear to see why inaction isn’t going to remain a viable response for very long.
Sap is released from broken stems or bristles and released from leaf bristles on contact even if they remain unbroken in the same way as a stinging nettle. So simply brushing past a plant with your bare skin could be sufficient to cause problems. The sap contains substances called furocoumarins which make skin photosensitive (very sensitive to light) this can result in a “burn” to your skin on contact and can blind you if it gets into your eyes. These substances are actually present in the sap of all members of the hogweed family but in much smaller quantities, sufficient to cause irritation rather than the severe effects of exposure to Giant Hogweed sap.
The “burn” effect is caused by severe irritation which results in photosensitivity, (fully described as Phytophotodermatitis) this will make the affected area extremely painful, with blistering occurring 24-48 hours after exposure and will probably result in dense pigmentation (purple scars). The effects of the photosensitivity may persist for years afterwards causing exposure to sunlight to be very painful. The scars can be extremely disfiguring and take months to heal and fade.
It is crucial to note that initial exposure to the sap is completely painless and the reaction is activated by ultraviolet radiation which can begin 15 minutes after contact and will peak 30 minutes to 2 hours after exposure. So if you think that you may have come into contact with Giant hogweed sap, wash the affected area thoroughly with soap and water immediately and keep the exposed area out of sunlight for 48 hours. If you know that you’ve been exposed or reactions do occur then seek medical attention, steps can be taken to reduce the severity of the reaction and ease discomfort and a quick response is strongly recommended.
The leaves contain more sap in June and the concentration of the active compounds will vary between plants but the only sensible option is to avoid contact between the plant and exposed skin and be aware that absorbent fabrics can soak up sap and allow the transfer of sap onto skin. Do not touch your face or rub your eyes if there is even the smallest chance that you have this sap on your hands or the outside of your protective clothing.
Everything you wanted to know about Giant Hogweed but were too afraid to ask
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