Oakmoss, or Evernia prunastri, is a lichen that grows on oaks (as well as some other trees) and is harvested to produce oakmoss absolute. The absolute is green or brown and is very thick; it has a wonderful earthy, mossy aroma with herbal and green nuances.
Oakmoss absolute is a skin allergen to a small percentage of people, so its usage is restricted to small amounts of the so-called low-atranol natural version, which is natural moss that is treated to remove nearly all the allergens atranol and chloroatranol. These days, synthetics are often used in addition to or instead of natural oakmoss. Many Sonoma Scent Studio scents contain low-atranol natural oakmoss (for example, Winter Woods, Incense Pure, Nostalgie, Forest Walk, Jour Ensoleille, Ambre Noir, Fireside Intense, and To Dream).
Note: Natural oakmoss is still allowed by IFRA rules as long as it is the kind that has had the allergens atranol and chloroatranol removed and as long as it is used at or below the IFRA percentage limits. This subject is still being discussed, however, and new rules could be adopted in the future. At the same time that regulators are studying appropriate atranol limits, scientists continue to improve their abilities to remove atranol to lower and lower levels of parts per billion, and continue to improve their detection methods to detect and measure the most minute quantities of atranol. We will have to wait to see where this all goes. Oakmoss is an extremely important perfumery ingredient, so much research is being done in this area.