In which situation should a wax treatment be postponed?

Postponing a wax treatment after recent sun exposure is advisable because the skin can be sensitive and more prone to irritation or damage after being exposed to UV rays. Waxing on recently sunburned or tanned skin can lead to increased discomfort, potential pain, and a higher risk of adverse reactions such as erythema (redness), swelling, or even skin peeling. Therefore, in cases where the client has had significant sun exposure, it is best to wait until the skin has returned to a normal state before proceeding with waxing.

Considering the other situations: while a client with a cold may feel uncomfortable, it wouldn't directly contraindicate the procedure. Fasting typically doesn't affect the appropriateness of waxing, and wearing makeup can usually be addressed by cleansing the skin prior to treatment. Hence, recent sun exposure represents a significant concern that justifies postponement of waxing.