Alpha-Isomethyl Ionone

What it is

Alpha-isomethyl ionone is a fragrance material with a floral, woody note reminiscent of violets. It is part of the perfume oil in a formulation and appears in the ingredient list under its own name rather than under the collective term “parfum”. The reason is a labelling rule covering a group of fragrance substances that can cause contact allergies in part of the population: above a certain amount in the product they have to be named individually.

Being named separately is therefore primarily an aid to recognition, not a warning about a general risk. Anyone sensitised to this fragrance can avoid it deliberately. For everyone else, the entry initially says only that it is present.

Why

• A labelling requirement is not a hazard warning. Being named means that this substance belongs to a group for which contact allergies are documented. It does not mean that the product is risky for the general population.
• Allergy and irritation are different things. A contact allergy is an immune reaction and presupposes previous sensitisation. It affects a minority, but in those people it is reproducible and can be triggered by very small amounts. That is precisely why naming the substance helps.
• Why the classification reads “increased attention”: not because of a general hazard, but because very small amounts can be enough in people who are already sensitised, and because the composition of a fragrance is otherwise not visible. The classification follows the substance group and expressly does not establish that the substance causes harm in its intended use.
• The form of application says more here than the name of the substance. In styling and straightening products the fragrance stays in the hair, so contact lasts longer than with a product that is rinsed out.
• For the salon the practical benefit is clearly defined: where a fragrance allergy is known, the substance can be found deliberately in the ingredient list. Without such a known allergy, the entry gives no reason to act.

When the assessment differs

• A documented allergy to this fragrance or to fragrances in general: the product is then unsuitable for that person. That is a statement about the person, not about the quality of the product.
• Pre-damaged, irritated or inflamed skin, and atopic dermatitis: uptake through a disrupted skin barrier is higher, and so is the likelihood of sensitisation.
• Products that stay in the hair compared with rinse-off products: longer contact and, where the scalp is involved, longer exposure of the skin.
• Occupational contact: working with fragranced products every day is a different exposure situation from a client every few weeks. Skin protection and gloves are the topic here, not the choice of product alone.
• Children and infants: not assessed here.

Open questions

• Concentration in the actual product: not available. Fragrance materials are usually used at low levels, but that does not replace a figure.
• Regulatory status: which fragrance substances must be named individually, and above what amount, is regulated and has been extended in recent years. Thresholds, the scope of the list and deadlines have not been checked here and are deliberately not quoted second-hand.
• Frequency of sensitisation in the population: evaluations from dermatological test series exist but have not been evaluated here. The classification follows the substance group.
• Natural occurrence: a database entry reports occurrence in yeast. It is not independently confirmed. It has no bearing on the origin of the raw material used in cosmetics, which is produced synthetically.
• Inhalation from spray products: not assessed. That would be a separate exposure route with its own data.

Sources for this assessment

• The Fragrance Conservatory (Fragrance Creators Association): alpha-Isomethyl-ionone — Herstellung im Labor. Branchennahe Fachorganisation, abgerufen am 08.09.2026.

Related substances

Applies to: Fragrance materials

• Benzyl Salicylate — Fragrance or declarable fragrance allergen
• Citronellol — Fragrance
• Limonene — Fragrance
• Linalool — Fragrance

Further substances from the same group for which a long-form assessment already exists.