Perhaps the self treatment technique would work also for real henna or lawsonia inermis
allergy (red hair dye). I have not tried and I have no idea about lawsonia inermis
I used this technique because I developed mild allergy on indigo which only showed on
my scalp as irritation, itching, hair break.
Official allergy treatment similar to mine is called sublingual immunotherapy,
but allergen is put under the tongue instead.
Attention: If you have serious allergy on indigo attacking your eyes, respiratory...
STAY AWAY FROM ALLERGEN, IT CAN BE DANGEROUS AND FATAL!!!