Is it safe to use neti pot for allergy.

Absolutely.: This is one of the prime reasons they are sold.

Neti Pot: Generally, use of the Neti Pot with sterilized/bottled, room temperature water is low risk. There has been a report of brain infection with use of tap water. Keeping the device clean/dry after use is important. Possible benefits may include reduction in pain medication use and mechanical removal of debris from the nasal passages.