Not only that, but woad has antiseptic/astringent properties, and might possibly help in the wound department (although I think it would struggle in the decapitation/disembowelling area!) Possibly the Britons discovered this by happy accident.
According to Culpeper, "An ointment made of the leaves stanches bleeding...is good in such ulcers as abound with moisture, and takes away the corroding and fretting humours; it cools inflammations..." Another book I have (Mrs Grieve, 1931) quotes Culpeper, and then says that it is too astringent to be taken internally. The RHS Encyclopaedia of Herbs says that Caesar and Pliny both wrote that the Britons painted themselves blue with woad. It was first mentioned in Chinese medicine in the 1590s, "and is often prescibed in large doses with apparently no ill-effects. In practice, high doses are needed to maintain high levels of active ingredients. Recent research suggests pronounced anti-viral effects."

By the way, the smell of its fermentation in the dyeing industry was so bad, that Elizabeth 1 banned the process within 5 miles (8km) of any of her palaces. I had some years ago in the garden. It has the most beautiful black seeds! It also got a bit straggly.

Andrea