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ALPHA-TERPINENE

CAS 99-86-5
55

Safety score · 0–100

Moderate

Derived from EU CosIng regulatory status, PubChem hazard data and published research. How we score.

A fragrance compound found in tea tree oil — EU-restricted because it oxidises rapidly in air to form skin-sensitising allergens.

Alpha-Terpinene (C₁₀H₁₆, CAS 99-86-5) is a monoterpene hydrocarbon found naturally in essential oils including tea tree, marjoram, and cardamom. Listed in EU Annex III/131 as a regulated fragrance allergen requiring mandatory labelling above 0.001% in leave-on and 0.01% in rinse-off products. Research demonstrates rapid autoxidation on air exposure, forming allylic epoxides and endoperoxides that are potent skin sensitisers. The peroxide value must remain below 10 mmoles/L. It functions as an antioxidant in its pure form but becomes increasingly allergenic with oxidation.

Skin benefits

  • Antioxidant properties in pure, non-oxidised form
  • Natural fragrance component

Known concerns

  • Known skin sensitiser when oxidised
  • EU Annex III restricted fragrance allergen
  • Rapidly autoxidises on air exposure
  • Oxidation products include potent allergens (epoxides, endoperoxides)
  • Can cause allergic contact dermatitis

References

EU

EU CosIng database

European Commission cosmetic ingredient registry: regulatory status, restrictions, authorised functions.

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This profile is for educational purposes and does not constitute medical advice. Regulatory status and scientific understanding evolve, so always read the physical product label and consult a healthcare professional for personal concerns.