Which ingredient is known for its stimulating effect on the skin but is not suitable for sensitive skin?

The ingredient known for its stimulating effect on the skin, which is not suitable for sensitive skin, is Fuller's earth. Fuller's earth is a natural clay that is commonly used in beauty treatments for its absorbent and exfoliating properties. It helps to draw out impurities and excess oil from the skin, making it popular for those with oily or acne-prone skin. However, its stimulating effect can also be quite strong, potentially leading to irritation for individuals with sensitive skin.

For those with sensitive skin, ingredients that are soothing and less aggressive are typically recommended. While ingredients like calamine and magnesium carbonate are often used for their calming or gentle properties, Fuller's earth may cause reactions such as redness or discomfort due to its active nature. Flowers of sulphur is also used for various skin conditions but is less recognized for stimulating effects compared to Fuller's earth. Thus, when working with clients who have sensitive skin, it’s crucial to consider the impact of more active ingredients like Fuller's earth.