The Truth About Fishy Smells and Omega-3

I'm not noticing a smell, is there something wrong with my omega-3?

Whilst noticing a marine-like smell when you open your vegan omega-3 is nothing to worry about, many people only report the mild, lemony flavour. Because Mighty Kids omega-3 is 100% plant-based, sourced from algae, it is an ideal, non-fishy alternative that is just as effective for supporting learning, thinking, and emotional regulation.

Fishy odours are produced by the oxidation process. This is harmless, but nonetheless, we still make sure that each and every bottle of omega-3 oil arrives extremely fresh. 

How can we be sure it's always fresh?

1. The TOTOX score of our omega oil

The TOTOX value of an oil is a reputable measurement of its overall freshness and quality.

It is the calculation of the total oxidation present, with scores ranging from 0 to 50. Industry standards recommend a maximum rating of 26, and our vegan omega-3 is scored between 7.45 and 12.45: well within the acceptable limits.

2. The time between harvesting and bottling 

Since the Mighty Kids omega-3 is manufactured specifically to order, and produced in a carefully controlled, lab environment rather than being harvested from the sea, the production time to bottling is minimal. This minimises any potential for oxidation to occur. To optimise purity, our omega-3 typically reaches customers within the same month it was harvested; it doesn't get much fresher than that!

3. Processes in place to mitigate the risk of oxidation

To reduce the risk of oxidation, we ensure only the freshest possible raw materials are used, and do not store any extra or leftover materials, ordering quantities aligned precisely with production needs. 

Although it is impossible to create a “ZERO oxidation oil" from something like omega, due to the nature of polyunsaturated fatty acids (essential, healthy fats), and the way they naturally interact with the environment, every possible care has been taken to minimise oxidation, and health risks are not associated with this level of normal oxidation.

A marine odour is only experienced by a small number of people, and does not mean that the supplement has gone off or been contaminated; it is just a harmless part of the oxidation process.

 

The science behind the smell

The molecular structure of omega-3s makes them prone to oxidation into volatile, odorous compounds, which can smell fishy even from entirely vegan sources, like ours at Mighty Kids.

Regardless of the source (fish or algae), the high number of double bonds in omega-3 fatty acids means that they are more likely to oxidise, which is the process of reacting with the air, causing small changes over time. When this happens, secondary oxidation products are formed, and it is these natural, breakdown compounds that can cause a noticeable smell, with notes often likened to seaweed or fish.¹

What breakdown products are responsible?

Experiments have confirmed that the by-products responsible for the fishy odour are a combination of:

• Heptanal 
• (E,Z)-3,5-octadien-2-one²

These are volatile compounds, evaporating easily, which is why they can be smelled so strongly even in tiny amounts. They are:

• Harmless at the levels found in oxidised oils
• Naturally occurring in many everyday foods, like oranges and corn 
• Regularly used in food flavour and aroma research

Is my omega-3 still safe to consume?

If these oxidation by-products are consumed, they will simply be excreted via one of:

• Sebum (the natural oils produced by your skin)
• Sweat
• Pulmonary excretion (getting rid of the smell-causing compounds by breathing them out; similar in mechanism to onion breath but typically fading much quicker!)

This explains why some individuals might notice a temporary odour (even when the oil itself does not taste or smell of anything) from their scalp, skin or breath. 

Odours are not due to:

Fish contamination

• Algae oils contain no fish proteins.

Microplastics, or heavy metals

• Neither of these are capable of producing volatile, fishy smells. Furthermore, our supplements contain no pollutants, contaminants, microplastics, or heavy metals.

Why do only some people notice a marine-like odour?

Individual oxidative stress levels³

People with higher antioxidant capacity experience less lipid oxidation, reducing the formation of volatile, odorous compounds. This can be due to a diet rich in antioxidants or naturally stronger endogenous defences (antioxidants and protective enzymes that the body produces).

Sebum production and skin microbiomes⁴

Individuals who produce fewer natural oils, or with different skin microbial compositions, may excrete fewer volatile compounds via their skin.

Genetic variability⁵

Different people have variations in certain lipid metabolism enzymes which alter both the rate and type of oxidative metabolites produced. Stronger compounds, or faster production could have an influence on noticeable smells.

In summary

For most people, the Mighty Kids Vegan Omega-3 supplement has a mild, lemony flavour, with an inoffensive, marine-like smell. A combination of individual differences, such as dietary antioxidants, skin microbiome, absorption, enzymatic metabolism, and dose taken can all explain why some individuals notice a slight odour with omega-3 supplementation while others do not. Importantly, any such smells noticed are harmless. Omega-3s are such crucial, beneficial nutrients, supporting growth, development and cognitive function, providing healthy fats that the brain and body needs but can't make on its own.

 

For the sciencey people

More on the molecular structure

Omega-3 fatty acids include EPA and DHA.

• EPA: eicosapentaenoic acid

• DHA: docosahexaenoic acid

These have a long-chain polyunsaturated molecular structure that is prone to oxidation.

Trimethylaminuria

 Trimethylaminuria (TMAU) is a metabolic disorder, known for causing the body to produce a strong, fishy odour. It is genetic, and cannot be caused by taking supplements.

• TMAU is very rare, involving nitrogen metabolism; the DHA/EPA oxidation produces aldehydes and ketones instead of amines.

Evidence limitations

It is extremely unlikely that supplements could play a role in producing odours in people. Currently, however, there are no PubMed systematic reviews or RCTs which directly and exclusively study omega-3 supplementation causing fishy body odour or smell as a primary outcome (especially for algae vs fish sources). 

Most of our current evidence on smell comes from mechanistic lab chemistry studies on oxidation of EPA/DHA and odour compound formation.

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References

1. Hammer, M., & Schieberle, P. (2013). Model studies on the key aroma compounds formed by an oxidative degradation of ω-3 fatty acids initiated by either copper(II) ions or lipoxygenase. Journal of agricultural and food chemistry, 61(46), 10891–10900. https://doi.org/10.1021/jf403827p
2. Marsili, R. T., & Laskonis, C. R. (2014). Odorant synergy effects as the cause of fishy malodors in algal marine oils. Journal of agricultural and food chemistry, 62(40), 9676–9682. https://doi.org/10.1021/jf502252q
3. Pizzino, G., Irrera, N., Cucinotta, M., Pallio, G., Mannino, F., Arcoraci, V., Squadrito, F., Altavilla, D., & Bitto, A. (2017). Oxidative Stress: Harms and Benefits for Human Health. Oxidative medicine and cellular longevity, 2017, 8416763. https://doi.org/10.1155/2017/8416763
4. Grice, E. A., & Segre, J. A. (2011). The skin microbiome. Nature reviews. Microbiology, 9(4), 244–253. https://doi.org/10.1038/nrmicro2537
5. Roussel, C., Lessard-Lord, J., Nallabelli, N., Muller, C., Flamand, N., Silvestri, C., & Di Marzo, V. (2025). Human Gut Microbes Produce EPA- and DHA-Derived Oxylipins, but not N-Acyl-Ethanolamines, From Fish Oil. FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 39(12), e70713. https://doi.org/10.1096/fj.202500752RR