Which of the following is a common side effect of retinoids?

Dryness and irritation are indeed common side effects of retinoids. Retinoids, which are derivatives of Vitamin A, work by promoting cell turnover and enhancing collagen production. While these actions can lead to clearer, more youthful-looking skin, they can also result in the skin becoming dry and irritated, particularly when first introduced into a skincare routine. It's not unusual for users to experience symptoms like flaking, redness, and a feeling of tightness, especially if they use retinoids too frequently or in high concentrations without allowing their skin to acclimate.

The other options present side effects that are less characteristic of retinoid use. Oily skin tends to be less common since retinoids can actually help regulate oil production in excess sebum conditions. Clogged pores may occur, but retinoids are generally effective at preventing and treating acne by keeping pores clear. Increased pigmentation is also not a typical side effect; in fact, retinoids are often used to reduce hyperpigmentation due to their ability to promote skin cell turnover and fade dark spots.