Leucine

What is Leucine?

Leucine is a naturally occurring essential amino acid, classified as one of the three branched-chain amino acids (BCAAs), with the chemical structure (2S)-2-amino-4-methylpentanoic acid. It is derived from protein hydrolysis or produced synthetically for use in personal care products. In cosmetics, leucine belongs to the category of conditioning agents and is commonly found in skincare creams, shampoos, and conditioners. It functions by adsorbing onto the skin or hair surface, forming a protective film that enhances moisture retention and reduces surface friction. This action helps maintain the skin's suppleness and improves hair's texture, while its mild perfuming properties help balance scent notes without overpowering the formula.

Comedogenic Rating 0/5 Low risk of clogging pores
EWG Safety Rating 1 View on EWG →
PubChem View on PubChem →

Roles in Formulation

This ingredient serves the following purposes in cosmetic formulations:

Fragrance ingredient
Contributes scent character and/or masks base odors, shaping the overall sensory experience of the formula (subject to allergen and IFRA considerations).
Hair conditioning
Improves softness, shine, and manageability by reducing friction and static; commonly achieved with cationic agents, silicones, oils, or conditioning polymers.
Skin conditioning agent
Maintains skin softness, smoothness, and flexibility.

Benefits

Supports skin softness and smoothness through conditioning action.

Enhances hair manageability by reducing friction and static.

Contributes to a balanced fragrance profile in products.

Who It's For

A quick guide for who this ingredient may suit (and who should be cautious).

Who May Benefit Who Should Avoid
Individuals with dry or rough skin seeking hydration support.
Those with known allergies to amino acids.
People with unmanageable or static-prone hair.
People experiencing irritation from protein-derived ingredients.
Users of scented cosmetics preferring subtle aroma enhancement.
Individuals sensitive to fragrance components in formulations.

Safety Notes

  • Rated low hazard overall with minimal health concerns.
  • Non-comedogenic, unlikely to clog pores.

Frequently Asked Questions about Leucine

What is leucine in cosmetics?

An essential amino acid used as a skin conditioner, hair conditioner, and fragrance ingredient to improve texture and scent.

Is leucine safe for daily use?

Yes, it carries a low safety rating and is gentle for most skin types when used as directed.

Does leucine clog pores?

No, it has a comedogenic rating of zero, making it suitable for acne-prone skin.