What might be a sign that a specific tanning product is unsuitable for a client?

A sign that a specific tanning product is unsuitable for a client is previous negative reactions. This indicates that the client has had adverse effects from the product in the past, such as rashes, irritation, or allergic responses. Such reactions suggest that the client may be sensitive or allergic to certain ingredients within the product. It’s crucial for a tanning professional to take into account any prior negative experiences a client has had with tanning products, as this can help prevent similar issues from occurring again. Safety and client comfort should always be prioritized in any tanning practice.

The other options do not accurately signal unsuitability. Immediate skin hydration is typically a desirable effect, celebrity endorsements do not provide any insight into the product's safety for a specific individual, and while long-lasting effects may seem ideal, they do not correlate with the client’s safety or suitability regarding specific reactions.