Ingredient review
Trans-2-Undecenal
INCI: TRANS-2-UNDECENAL
Trans-2-Undecenal is a synthetic fragrance ingredient that adds a fresh, citrusy note to products, but may cause irritation in sensitive individuals.
In plain English
Trans-2-Undecenal is a man-made chemical that smells fresh and citrusy, like green leaves or cucumber. It's added to skincare and beauty products to make them smell nice. Because it's a fragrance ingredient, it can sometimes irritate sensitive skin, especially if you're prone to allergies from scents.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Main practical flags: irritation is moderate; clogging risk is low.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- moderate
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Trans-2-Undecenal can be useful, but watch for some irritation potential.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging Trans-2-Undecenal.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
moderateCan bother some users, especially with frequent use, damaged skin, or strong companion ingredients.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
Trans-2-Undecenal is a synthetic aldehyde compound used primarily as a fragrance ingredient in cosmetics and personal care products. It belongs to a class of chemicals known for their strong, pleasant odors.
How it works
In a cosmetic product, Trans-2-Undecenal works by releasing a volatile scent that interacts with olfactory receptors in the nose, providing a fresh, green, citrus-like fragrance. It does not have a functional skincare benefit beyond scent.
Pros
Pleasant scent
Adds a fresh, citrusy fragrance that can make skincare routines more enjoyable.
Low comedogenic risk
Unlikely to clog pores, making it suitable for most skin types in terms of acne.
Cons and cautions
Potential irritant
Can cause redness, itching, or stinging in people with sensitive skin or fragrance allergies.
No skincare benefit
Does not hydrate, protect, or improve skin health; it only provides scent.
Best for
- People who enjoy scented skincare products
- Those without known fragrance allergies
Use caution if
- Individuals with sensitive or reactive skin
- People with known fragrance allergies or contact dermatitis
Usage tips
Safety summary
Trans-2-Undecenal is generally safe for most people at low concentrations, but it can cause skin irritation and allergic reactions in sensitive individuals. It is not considered a major health concern by regulators.
Research notes
Research indicates that Trans-2-Undecenal is a known skin sensitizer in some individuals, but it is considered safe for use in cosmetics at regulated levels. Studies focus on its allergenic potential rather than long-term health effects.
Common label clues
- Typical concentration
- Typically used at very low concentrations (under 1%) due to its strong scent.
- Regulatory status
- Approved for use in cosmetics in the US and EU, but must be listed as a fragrance allergen in the EU if present above 0.01% in leave-on products or 0.001% in rinse-off products.
- Common uses
- Fragranced skincare, Perfumes, Body lotions, Cleansers
- Environmental note
- As a synthetic compound, its environmental impact is minimal at typical usage levels, but it is not biodegradable in all conditions.
Good to know
- Trans-2-Undecenal is often listed simply as 'fragrance' or 'parfum' on ingredient labels.
- It is regulated as a fragrance allergen in the EU, requiring labeling if above certain concentrations.
Common questions
What is Trans-2-Undecenal in beauty products?
Trans-2-Undecenal is a man-made chemical that smells fresh and citrusy, like green leaves or cucumber. It's added to skincare and beauty products to make them smell nice. Because it's a fragrance ingredient, it can sometimes irritate sensitive skin, especially if you're prone to allergies from scents.
What does Trans-2-Undecenal do in a beauty product?
In a cosmetic product, Trans-2-Undecenal works by releasing a volatile scent that interacts with olfactory receptors in the nose, providing a fresh, green, citrus-like fragrance. It does not have a functional skincare benefit beyond scent.
Is Trans-2-Undecenal safe for most people?
Trans-2-Undecenal is generally safe for most people at low concentrations, but it can cause skin irritation and allergic reactions in sensitive individuals. It is not considered a major health concern by regulators.
Who should be careful with Trans-2-Undecenal?
Individuals with sensitive or reactive skin People with known fragrance allergies or contact dermatitis
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.