Which type of lightener contains oxygen-releasing boosters and is typically too strong for scalp use?

The correct choice is powder lighteners because they are designed to be mixed with a developer that contains hydrogen peroxide, which releases oxygen. This chemical reaction enhances the lightening process but results in a formulation that can be potent and too harsh for direct application on the scalp. The strong concentration of the active ingredients in powder lighteners can lead to discomfort or irritation when applied to sensitive areas, making them more suitable for application on strands of hair rather than directly on the scalp.

In comparison, paste, liquid, and gel lighteners have different consistencies and formulations that make them generally milder and more manageable for scalp use. Paste lighteners are thick and often used for precision applications, liquid lighteners are typically formulated for ease of application but are less concentrated than powders, and gel lighteners provide a smooth application while also being gentler on the scalp. This differential in formulation is what establishes powder lighteners as the strongest option, thereby affirming their designation as typically unsuitable for scalp application.