Following the ECJ’s ruling in the 2001 Ralf Sieckmann case, courts have continued to support the view that it is not possible to register smells or sounds as trademarks. A smell cannot be adequately graphically represented by a verbal description because it is too imprecise. Manufactured smells (which would include scents and perfumes) can give rise to intellectual property rights which will generally attach to the information describing the ingredients of / or formulae for the smells or to the processes of production (or both). This type of information has traditionally been protected by treating it as a trade secret.
By way of analogy, take for example the ingredients for the most famous brand in the world of soft drink. This information has always been guarded by the company as a trade secret and its disclosure to employees or third parties has always been under the form of non-disclosure agreements. Trade secrets are generally enforced by contract.
The advantage of holding a trade secret is that the intellectual property rights can exist indefinitely so long as you manage to keep it a secret. The trick is to make sure that you have sufficient contracts in place (whether with your employees or contract manufacturers or other third parties) to allow you to disclose freely the ingredients and means of production of your scents on a need to know basis. Any misuse or unauthorized disclosure of a trade secret by a contracted party would generally amount to a breach of contract and an actionable claim in the courts, giving the holder the right to an injunctive remedy (where available) and possible recovery of damages.