A patch test is a small dab of a product, such as a lash tint, brow tint, hair colour or lash adhesive, put on a discreet patch of skin some time before the full service. If there is a reaction, the service does not go ahead with that product. Many manufacturers tell you to test before every service with their product, or before the first one, and say how long beforehand; 48 hours is common for tints and colours. Your insurer may have its own requirement as well. Follow the instructions for the product you use and the conditions of your policy, and record every test.
What a reaction means, and what the client should do about it, is a question for their doctor or pharmacist, not for whoever takes the booking.
In practice
A lash and brow studio asks for a patch test 48 hours before any first tint or lamination. It lists the test on its menu at $0 for 10 minutes so clients can book it, and its booking rule is simple: a first-time tint request gets two appointments, the test and the service, at least two days apart. In one month the studio books 26 first-time tints. Twenty-four clients come in for the test and keep their service two days later. The two who missed the test are offered a new test date rather than tinted on the day.
Record the date, the product and the result on the client card. When the client comes back in six weeks, that record tells you whether the product's instructions call for another test.
In Glow Line
List the patch test as a service, even at $0, and write your rule in notes, including how far ahead of the service it must be. The assistant states your rule and never answers a health question; it says the team will confirm. See services and hours.