Name a common ingredient found in PMU pigment formulations that may cause allergic reactions.

Iron oxide is a widely used ingredient in PMU pigment formulations and is known to be a potential allergen for some individuals. It provides rich, stable colors and is often favored for its durability and natural appearance. However, some people may develop sensitivities or allergic reactions to iron oxide due to their unique body chemistry. This is particularly relevant in cosmetic applications where the pigment is introduced into the skin.

While other ingredients like glycerin, alcohol, and lanolin are also present in various formulations, they generally do not have the same level of documented allergenic potential in the context of permanent makeup. Glycerin is often used for its moisturizing properties, alcohol serves primarily as a preservative or solvent, and lanolin is commonly included for its emollient benefits. However, iron oxide specifically stands out as a significant allergenic concern for certain clients, which is why it is the correct answer in this context. Understanding these potential reactions can help practitioners make informed decisions and choose suitable products for their clients.