And late-onset (three days to six weeks) symptoms include swollen glands, high temperatures, mouth ulcers and painful skin blisters.

Some people find its sap can cause skin blisters, although nowhere near as badly as giant hogweed, so wear gloves and avoid sap splashes.

An over-the-counter anti-inflammatory such as ibuprofen can help with the pain and swelling, but if your skin blisters and you feel unwell seek medical advice.

The stems are reddish and contain a milky latex capable of causing skin blisters.

Direct scarring moxibustion places a small cone of moxa on the skin at an acupuncture point and burns it until the skin blisters, which then scars after it heals.