i found this on henna side effects:
Henna seems to be safe for most adults 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.
so, there can be some side effects...and i also know that you have to take care with tatoos if you color your hair with henna
but, you could use natural hair die without having to worry about henna side effects- i don`t know if you`ve heard about iHerb, but you cand find loads of 100% natural amazing products- i buy my hair die and other cool stuff there...and...you will save $5 on your first order on iHerb, if you use the code ANO508- you can try this it works...
bye