All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It appears – Allaah Knows best – that it is permissible to use lemon juice for the purpose which you mentioned in the question, as some scholars permitted the use of some foods in order to get rid of the harm of the Noorah (slaked lime used for hair removal) and its effect after removing the hair.
Ibn Al-Muflih from the Hanbali School, said: “A little bit of colocynth pulp should be mixed with the Noorah to avoid itching in the places in the skin where the Noorah was applied, and then henna and safflower should be applied in order to cool the body and get rid of the freckles.”
He also said: “It should also be anointed with pansy, rose water, safflower, watermelon seeds, and rice flour mixed with rose water.” Also, some of them said: “Its place should be anointed with henna, and after a while it (the Noorah) should be drizzled (little by little on the skin), then it should be anointed with fat mixed with lentil flour, vinegar and cold water.”
However, it is more appropriate to avoid this, and look for a product other than food so that the objective would be achieved and the harm is avoided.
Allaah Knows best.