Why do clinical antiperspirants sting or itch?

The higher aluminum chloride concentration that makes a product effective also raises irritation risk, especially on freshly shaved skin. Reviewers across the threads we read for Certain Dri and SweatBlock describe a sting on first use that typically fades after a few applications. Applying to fully dry skin, avoiding application immediately after shaving, and starting with every-other-night use are the most common community workarounds.