ISOLEUCINE

Description: ISOLEUCINE — amino acid, part of the skin natural moisturizing factor (NMF).

All Functions: amino acid, part of the skin natural moisturizing factor (NMF)

Quick Facts:

• Category: humectant

Proven Benefits At A Glance:

• Isoleucine is an essential amino acid—your body can’t make it, so you need it from food or supplements
• Research in fish shows dietary isoleucine may support skin barrier function and antimicrobial defenses
• One study linked elevated isoleucine from certain bacteria to cardiovascular concerns in animal models, though this involves a specific pathogenic pathway
• Isoleucine is produced industrially as a safe nutritional additive for animal feed
• Isoleucine deficiency in animal studies was associated with eye and skin issues and reduced resistance to microbes

Safety tier is a starting heuristic from regulatory status and comedogenic rating, not a dermatological verdict — see our Terms for the full disclaimer. Research confidence reflects how many real cited studies back this ingredient, not the strength of their findings.

🧪 ISOLEUCINE

ISOLEUCINE

CAS Number: 73-32-5 / 443-79-8

Also Known As: —

Category: humectant

EC Number: 200-798-2 / 207-139-8

Korean Name: 아이소류신

L-Isoleucine; DL-allo-Isoleucine; 2-Amino-3-methylpentanoic acid

ISOLEUCINE is a humectant ingredient used in skincare formulations.

🌍 Regulatory Status

📊 Comedogenicity

📚 Research & Evidence

🔬 The Science

Isoleucine is one of nine essential amino acids, meaning humans must obtain it through diet because our bodies cannot synthesize it. Here’s what the research actually shows:

#1: **Skin barrier support**: In a 2020 study of hybrid catfish (Fish Physiol Biochem), dietary isoleucine increased mucus protein content, antimicrobial activity against five bacterial species, and boosted skin immune markers including complement proteins and antibodies. The same study found isoleucine reduced oxidative stress markers (ROS and malondialdehyde) and improved tight junction proteins that maintain the physical skin barrier. However, this research is in fish, not humans, so direct translation to human skincare remains unclear.

#2: **Cardiovascular concerns in specific contexts**: A 2026 study in *Arterioscler Thromb Vasc Biol* identified an unexpected pathway where isoleucine derived from *Fusobacterium nucleatum* (a pathogenic oral bacterium) promoted harmful cell death (ferroptosis) in blood vessel smooth muscle cells in mice with aortic aneurysm. Notably, the researchers found that restricting dietary isoleucine reduced this effect. This is mechanistically interesting but describes a disease-specific interaction in animal models involving a pathogenic bacteria—not a general concern about isoleucine itself in healthy people. #3: **Deficiency effects**: A 1984 study in *Br J Nutr* showed that severe isoleucine deficiency in kittens (below 2.2–3.8 g/kg diet) led to crusty eye exudates and increased susceptibility to staphylococcal skin infection, suggesting impaired immune or barrier function.

This highlights isoleucine’s role in host defense, though again in animal models. #4: **Safety as a supplement**: The European Food Safety Authority (EFSA J, 2020) evaluated l-isoleucine produced by fermentation and concluded it is safe for target animal species, consumers, and the environment, with no skin irritation or sensitization concerns. The sources are limited to animal studies and safety assessments; direct human skincare claims are not supported by these abstracts.

💧 Skin Type Compatibility

⚠️ Don’t Combine With

🧴 Products Containing ISOLEUCINE

• BCL Kansosan Skincare Moisture Base AQ
• RETINOL RETINOL SKIN CREAM
• MyProtein Hair & body wash
• Bioélixire Odżywka do włosów zniszczonych
• Tío Nacho Tío Nacho Anti-Caida Engrosador
• marc anthony argan shampoo
• Pacifica Cosmic Hemp Balancing Face Wash
• NIOD Multi-Molecular Hyaluronic Complex (MMHC2)
• The Ordinary The Ordinary Glycolic Acid 7% Toning Solution (Solução tonificante de ácido glicólico 7%)
• ordinary suncream
• dr groot shampoo
• Paul Mitchell Paul Mitchell Awapuhi Shampoo
• collagen face mask
• OPLAPLEX Leave In – Numéro 5
• Sephora Beauty insider
• Olaplex No. 8 Bond Intense Moisture Mask
• FILORGA TIME-FILLER Crème Absolue Correction Rides
• Klorane Bébé Crème lavante nourrissante cold cream
• Klorane Klorane Bébé Baume corps au cold cream
• Klorane Klorane Bébé Crème hydratante Physio Calenduline

📄 Related Research

Matched by search — not necessarily verified support for every statement above.

• Chen L et al. (2026). Fusobacterium nucleatum-Derived Isoleucine Exacerbates Aneurysm by Inducing Ferroptosis in Vascular Smooth Muscle Cells. Arterioscler Thromb Vasc Biol.
• Hargrove DM et al. (1984). Leucine and isoleucine requirements of the kitten. Br J Nutr.
• Isogai S et al. (2022). High-Level Production of Isoleucine and Fusel Alcohol by Expression of the Feedback Inhibition-Insensitive Threonine Deaminase in Saccharomyces cerevisiae. Appl Environ Microbiol.
• Yin L et al. (2020). Effect of dietary isoleucine on skin mucus barrier and epithelial physical barrier functions of hybrid bagrid catfish Pelteobagrus vachelli × Leiocassis longirostris. Fish Physiol Biochem.
• EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) et al. (2020). Safety and efficacy of l-isoleucine produced by fermentation with Corynebacterium glutamicum KCCM 80189 for all animal species. EFSA J.