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Chemical Reaction: A Deep Breath

By: Steve Herman
Posted: December 10, 2008

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Where WoE is Weight of Evidence, NESIL is No Expected Sensitization Induction Level, and SAF is the Sensitization Assessment Factor.

The potential for sensitization is derived from many areas—including the LLNA (Local Lymph Node Assay), which is a fully validated test for determining the potency of skin sensitizing chemicals. Dosage is a critical factor in evaluating safe use using QRA. The full scope of QRA looks very complicated to a nonspecialist, but these acronyms and mathematical relations are simply a glimpse at the machinery that generates the current categories and allowable use levels. They are the answer to the question “Where did those numbers come from?”

Down to Smell

The most important feature of fragrance is smell, and it is there that a strange situation arises. There is precious little information on what happens when we inhale fragrance. At the beginning of RIFM’s testing history, it was obvious that the most important route of exposure was through leave-on skin products—and, of course eye contact, should it happen. Breathing fragrances involves few molecules and is very transitory, so it was considered a minor issue.

A great change in fragrance use occurred in the 1990s, with a profusion of fragranced candles and plug-in air fresheners. All this fragrance in the air directed attention to the potential respiratory consequences, and we were made painfully aware of how little was known about this topic.

RIFM began a respiratory program several years ago. Since more than 2,000 chemicals are used in fragrance, it is impractical to start by testing them all. A surrogate formula was constructed (Figure 2) based on structural alerts, volume of use and likeliness to be used in an air freshener. Starting a program from scratch that will ultimately lead to publication in peer reviewed journals and then to be the basis of guidelines or standards is no small matter, and the RIFM respiratory program has a timelime currently stretching to 2011.