A wax formula for the underarms should be selected according to hair:

The correct choice focuses on the texture of the hair when selecting a wax formula for the underarms. Hair texture can significantly influence the effectiveness of waxing, as different textures may require different types of wax for optimal results. For instance, coarse hair might respond better to a stronger, more adhesive wax that can grip the hair effectively, while finer hairs might be better suited to a gentler formula. Considering hair texture helps ensure that the wax can remove hair efficiently while minimizing discomfort for the client.

In contrast, other factors such as color, shape, and length do not directly impact the choice of wax in the same way that texture does. While they may have some relevance in the overall hair removal process—like selecting techniques or post-care products—they are not the primary considerations when choosing the right wax formula. Ensuring the wax matches the hair texture can lead to a smoother and more effective hair removal experience.