Fixatives are not a shortcut to longevity. They are a structural requirement. Without them, a formula has no Act 3.
A fixative in perfumery is a material — natural or synthetic — whose primary function is to slow the evaporation of more volatile aromatic compounds and extend the overall longevity of the formula. Fixatives operate in two ways.
Some act as chemical retarders: their own low volatility and molecular weight creates a kind of drag on the lighter molecules blended with them. Others function as blenders — they do not dramatically extend longevity but smooth the transitions between note tiers and give coherence to the overall structure.
Classical natural fixatives include musks, ambergris, labdanum, benzoin, and civet. Synthetic fixatives include Iso E Super, Ambroxan, Habanolide, and Exaltolide — each with different olfactory profiles and different mechanisms of fixation. The base of a well-formulated perfume is, essentially, a fixative system.
FACTS
RSC Chemistry of Fragrances explains the chemistry of fixation: high molecular weight compounds with low vapour pressure retard the evaporation of smaller, more volatile molecules by modifying the partial pressures of the system.
Benzyl benzoate — widely used as both a fixative and a carrier — functions on this principle.
Groom (The Perfume Handbook) documents the historical shift from natural animal fixatives (musk, civet, ambergris, castoreum) to synthetic alternatives, driven by both cost and IFRA restriction.
Piesse (The Art of Perfumery, 1879) identifies fixation as the fundamental structural problem of perfumery: the challenge is not creating a pleasant scent, but creating one that does not vanish in minutes — and he lists fixation as the primary technical skill of the perfumer.

TAKEAWAY
A formula without fixatives will perform well on a blotter (aka paper) and fail on skin. The fixative system — the base — is what determines whether a perfume reaches 2 hours or 12. When evaluating a new perfume, Act 3 performance is a direct measure of the fixative system's quality and design. If a fragrance has no Act 3, it is not fixed adequately for the concentration it claims.
