Ask a RIFM Scientist

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What is skin sensitization and why study it?

Isabelle Lee, PhD

Skin sensitization is one of the seven endpoints (six human health plus environmental) that the Research Institute for Fragrance Materials (RIFM) covers in its fragrance ingredient safety assessments. Skin sensitization refers to a substance’s potential to cause an immune response like red, bumpy, or itchy skin over time and after repeated exposure. Once a specific substance has sensitized a person’s immune system, they may continue to experience an allergic reaction to it, sometimes at lower levels of exposure.

RIFM is committed to the health of the body’s largest organ and its impact on overall health and quality of life. So many fragranced products—moisturizers, sunscreens, deodorants, and more—come into direct contact with our skin. This direct contact makes it essential to conduct safety evaluations for skin sensitization and ensure that they reflect accurate, real-world exposure levels.

As with the other endpoints, RIFM’s skin team follows the Criteria Document for discrete materials and the NCS Criteria Document for Natural Complex Substances (NCS), which outline the stepwise process to assess the skin sensitization potential of fragrance ingredients.

Risk management measures may be required when RIFM identifies a fragrance ingredient with sensitization potential. This process follows a risk assessment approach called the quantitative risk assessment for dermal sensitization of fragrance ingredients (QRA2) that includes deriving the No Expected Sensitization Induction Level (NESIL), the amount of a particular fragrance ingredient that someone can apply on their skin without causing skin sensitization. Additionally, RIFM calculates the Maximum Acceptable Concentration (MAC) values for several categories, like consumer products applied to the lips, products applied to the hair with hand contact, aerosol air fresheners, and many more. The International Fragrance Association (IFRA) then sets the IFRA Standards based on these MAC values. The Standards may ban, limit, or set criteria for using certain ingredients based on scientific evidence.

Senior Scientist Isabelle Lee, PhD, leads RIFM’s Skin Sensitization safety assessment and research programs.