Isoleucine at a glance

  • An essential amino acid that provides hydrating benefits
  • Plays a role in maintaining collagen and elastin (when consumed)
  • Works with other amino acids to maintain skin’s barrier
  • May be animal-derived or synthetic

Isoleucine description

Isoleucine is an essential amino acid that has slight humectant (water-binding) properties for skin. It’s considered essential since the human body cannot make isoleucine and so it must be obtained via foods or supplements. Isoleucine works with other amino acids to help maintain skin’s barrier and initiate surface repair so skin looks healthier. It is often combined with several amino acids for enhanced benefits. This amino acid may be animal-derived or synthetic (Paula’s Choice uses the latter) and its typical concentration in skin care ranges from 0.0003–0.002%, as very little of this ingredient is needed in order for skin to benefit.

Isoleucine references

  • Molecules, August 2021, pages 1–43
  • International Journal of Toxicology, November-December 2013, pages 41S–64S
  • Amino Acids, April 2012, pages 2,481–2,489

Peer-reviewed, substantiated scientific research is used to assess ingredients in this dictionary. Regulations regarding constraints, permitted concentration levels and availability vary by country and region.

Ingredient ratings


Proven and supported by independent studies. Outstanding active ingredient for most skin types or concerns.


Necessary to improve a formula's texture, stability, or penetration.


Generally non-irritating but may have aesthetic, stability, or other issues that limit its usefulness.


There is a likelihood of irritation. Risk increases when combined with other problematic ingredients.


May cause irritation, inflammation, dryness, etc. May offer benefit in some capability but overall, proven to do more harm than good.


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Not Rated