Which plant, widespread in Britain, if touched, causes a serious chemical reaction which makes skin hypersensitive to ultraviolet light?

The enormous hogweed was introduced to the UK from Central Asia in 1893, and it is currently found on river banks, canal towpaths, forest, and heathland. What effect does it have on you? Photodermatitis is caused by chemicals in the plant, which makes the skin sensitive to ultraviolet light from the sun and other sources.