What should be done if a client reports no stinging sensation from a new serum?

If a client reports no stinging sensation from a new serum, it suggests that the formulation may not possess enough potency or active ingredients to produce a noticeable reaction on the skin. A stinging sensation can often indicate that the active ingredients in the serum are effectively penetrating the skin and eliciting a response. Therefore, if there is no sensation, it may mean that the serum is too weak for the client's skin type or condition.

In contrast, if the serum was too strong, the client would likely experience discomfort or irritation, which would not correspond with the absence of sensation. Similarly, weakening the serum would not explain the lack of sensation; instead, it would further decrease the effectiveness of an already minimally potent product. Finally, replacing the serum would typically be reserved for instances where there is an evident defect or an adverse reaction, which is not the case here. Thus, interpreting the absence of a stinging sensation indicates that the serum is probably too weak for the client's needs.