The omega-3 index is a blood test that measures the percentage of EPA and DHA — the two long-chain omega-3 fatty acids — in the membranes of your red blood cells. It's the most reliable long-term marker of omega-3 status in the body.
Harris and colleagues at the University of South Dakota developed and validated the test, showing it correlates with tissue omega-3 concentrations far better than a serum measurement (Harris, 2008). The number is expressed as a percentage — most Americans sit in the 4-5% range; the range associated with cardiovascular protection is 8% or higher.
For skin, omega-3 status matters because EPA and DHA are structural components of every cell membrane — including skin cells. Pilkington and colleagues at the University of Manchester summarized the dermatology-specific evidence: adequate omega-3 supports barrier function, modulates inflammatory tone, and provides some photoprotective benefit (Pilkington, 2011).
Low omega-3 shows up on skin as increased transepidermal water loss (dryness that moisturizer doesn't fully fix), heightened inflammatory reactivity, slower barrier repair, and often worsened rosacea symptoms.
Repletion is straightforward. Fatty fish two to three times per week, or a supplement providing 2-3 grams combined EPA + DHA daily, typically raises the index into the target range within three to four months.
The omega-3 index is one of the nine biomarkers on the JenSkin panel.