*Ancient Blue is made from natural Indigo to create the look of Celtic Blue or Woading. ( Lasts three days to a week depending on positioning of the design on the body ) There has been no evidence of of toxicity or allergic reaction or harm from Indigo and it Indigo is approved by the FDA in its purified state. However as the Indigo is captured in an alkaline plant vat batches may vary so the safety of this product cannot be determined. To avoid sensitivity or allergies if you allergic to anything blue e.g. berries etc or have sensitive first do a skin test and only cover 10% of your body.