another google result

http://www.webmd.com/vitamins-supplements/ingredientmono-854-HENNA.aspx?activeIngredientId=854&activeIngredientName=HENNA&source=3

Henna seems to be safe for most people when used on the skin or hair. It can cause some side effects such as inflammation of the skin (dermatitis), including redness, itching, burning, swelling, scaling, broken skin, blisters, and scarring of the skin. Rarely, allergic reactions can occur such as hives, runny nose, wheezing, and asthma.

Henna is considered to be unsafe when taken by mouth. Accidentally swallowing henna requires prompt medical attention. It can cause stomach upset and other side effects.

Henna is considered unsafe for use in children, especially in infants. There have been cases of serious side effects, including blood disorders, when henna was applied to the skin of infants.

Do not use henna if:
You are pregnant or breast-feeding.
You have a disorder known as glucose-6-phosphate deficiency.
Use of henna in infants with glucose-6-phosphate deficiency has been reported to cause red blood cells to burst (hemolysis).

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• I didn't see it cause cancer in your googled result -640904- ♀ (0 bytes) () 05/25/2010 postreply 15:27:49