Which of the following is a common side effect after laser hair removal?

Redness at the treatment site is a common side effect after laser hair removal because the procedure uses concentrated light to target hair follicles, which can cause temporary inflammation in the skin. This redness is typically a result of the heat generated during the treatment and may last for a few hours to a couple of days. It's a normal response as the skin adjusts and heals following the exposure to laser energy.

While other side effects such as infection can occur, they are less common and usually result from improper aftercare or technician error. Headaches are not directly associated with the procedure, as laser hair removal primarily affects the skin surface. Long-term hair growth is contrary to the purpose of the treatment, which aims to reduce or eliminate hair. Therefore, redness at the treatment site stands out as the most typical and expected reaction following the procedure.