Botanical atlas

Woad

Isatis tinctoria

Long before synthetic dyes existed, woad was the great blue of the old world, the plant that colored the robes of medieval merchants and, according to Julius Caesar's own account, painted the bodies of ancient British warriors before battle. Its leaves hold a compound called indican, which turns a startling indigo blue through fermentation, and entire regions of France, Germany, and England once built their economies around dye vats full of woad. Beyond the dye pot, folk herbalists in Europe applied bruised or infused woad leaf to wounds and skin troubles, while related Isatis species have long held a place in Chinese herbal tradition as a cooling remedy taken during fevers and the cold and flu season. It is a plant with two lives, one as a working dye, one as a quiet household remedy, and both stretch back thousands of years.

Safety.

Concentrated internal use, as with indigo extracts used medicinally, has been linked to liver enzyme changes and rare liver toxicity, especially with prolonged or high-dose use. Avoid during pregnancy and breastfeeding, and use caution with liver disease.