Reviewed by Jessie, BSc Biomedical Science · Formulation Lead, Purest Kids
TL;DR — Oxidised omega-3 may be pro-inflammatory rather than anti-inflammatory, reversing the benefit you're paying for. A 2015 review found a substantial share of fish oils exceeded international oxidation thresholds. Smell is the fastest home check: fresh oil smells mildly oceanic; a strongly fishy, rancid, or musty odour indicates oxidation has begun.
The problem nobody talks about
Most of the conversation around omega-3 quality focuses on dose, source, and form. There is a fourth quality dimension that receives less attention but matters just as much: oxidation state. Omega-3 fatty acids are polyunsaturated, which means they are chemically reactive. When exposed to oxygen, light, or heat, they oxidise — and oxidised fish oil is not the same product as fresh fish oil.
What oxidation does to omega-3
Oxidised omega-3 oil contains lipid peroxides and aldehydes — breakdown products that are not biologically equivalent to intact DHA and EPA. Some research suggests that consuming oxidised fish oil may actually be pro-inflammatory rather than anti-inflammatory, essentially reversing one of the primary reasons for taking it. A 2015 review found that a substantial proportion of commercially available fish oil supplements exceeded international oxidation thresholds.
How to tell if your supplement has oxidised
The most obvious indicator is smell. Fresh, high-quality fish oil should smell mild — at most faintly oceanic. An unpleasant fishy, rancid, or "off" smell is a strong indicator of oxidation. The same applies to algae oil, though oxidised algae oil tends to smell less dramatically "fishy" and more generally musty or unpleasant.
For encapsulated softgels, you can bite one open and assess the smell of the oil directly. If a softgel supplement reliably smells bad, the oil is likely at least partially oxidised.
How to store omega-3 correctly
The enemies of omega-3 stability are oxygen, heat, and light. Keep softgels in a cool, dry place away from direct sunlight. Once opened, use within the stated shelf life. Do not leave the bottle in a hot car, near a stove, or in a sunny windowsill. Refrigeration can extend shelf life for liquid fish oil products.
Why this is less of an issue with softgels
The softgel format — whether fish oil or algae oil — provides a meaningful layer of oxidation protection. The oil is enclosed in a sealed shell that limits oxygen exposure until the moment of consumption. This is one reason why softgel formats have an oxidation advantage over liquid fish oils, which are exposed to air every time the bottle is opened.
Purest Kids Omega-3 Mango Burstlets are individually sealed softgels. Each burstlet contains oil that has been protected from air and light in its own shell until you bite into it. This is not incidental to the format — it is part of why the format was chosen.
Omega-3 Mango Burstlets — fresh, sealed softgel format →
References
- Jackowski SA, et al. "Oxidation levels of North American over-the-counter n-3 (omega-3) supplements and the influence of supplement formulation and delivery form on evaluating oxidative safety." Journal of Nutritional Science, 2015.
- Albert BB, et al. "Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA." Scientific Reports, 2015.
- Rowe CA, et al. "Fish oil increases oxidative stress compared with safflower oil in untrained adult male subjects." Journal of Lipid Research, 2016.