Fish sauce is the salty, amber liquid drawn off fish – usually anchovies – that have been fermented with a large amount of salt for many months. It is a basic seasoning across Southeast Asia: nước mắm in Vietnam, nam pla in Thailand, patis in the Philippines; Korea has its own anchovy sauces, Italy has colatura di alici, and the ancient Romans made fish sauces they called garum. A spoonful adds deep savory flavor (umami) and saltiness to dressings, dipping sauces, soups and stir-fries.
How Fish Sauce Is Made
Whole small fish are mixed or layered with salt and left in tanks or barrels. Over months, enzymes from the fish themselves and salt-tolerant microbes break the proteins down into peptides and amino acids – the source of the savory taste – while lipid oxidation and microbial metabolism build the characteristic aroma (Han et al., 2023). The liquid that collects is drawn off, filtered and bottled; some producers then add water or brine to the remaining fish for lower grades. Because so much depends on the microbes, industrial producers find the traditional flavor hard to control (Han et al.).
Fermented fish appears across Southeast Asia in thicker forms too – see Cambodia’s prahok, the region’s shrimp pastes, and Italy’s anchovy colatura di alici.
Histamine: The Hidden Hazard
The salt in fish sauce stops most harmful bacteria, but it doesn’t remove histamine. Histamine forms when bacteria break down an amino acid in the flesh of certain fish – anchovies, sardines, herring, mackerel and tuna among them – mostly when the fish aren’t kept cold after they are caught. It isn’t destroyed by cooking, and too much causes “scombroid” poisoning: flushing, headache, a burning mouth, cramps and diarrhea, usually within minutes to hours. Fish sauces have been recalled in Australia for high histamine, and the international Codex standard sets a maximum of 40 mg per 100 g of fish sauce (FSANZ).
Testing finds histamine in fish sauce routinely. It was present in all 15 Vietnamese traditional fish sauces in one study, though retail samples stayed under the EU limit (Pham et al., 2025); in a survey of 38 commercial fish sauces sold in Taiwan, several Korean samples exceeded the local limit (Huang et al., 2025).
That is why we don’t give a home fish-sauce recipe. A home batch ferments for many months at warm temperatures, its histamine depends on how fresh and cold the fish were before salting, and there is no way to measure it in a kitchen. Buy fish sauce from a producer whose product is tested, and keep it for seasoning.
How to Choose a Bottle
- Ingredients: the simplest list is fish (usually anchovy) and salt. Some brands add sugar, flavor enhancers or preservatives; the Taiwan survey found preservatives above the permitted level in several products (Huang et al., 2025).
- °N (degrees nitrogen): some labels show a number such as 30°N or 40°N. It measures nitrogen, a proxy for protein: a higher number means more protein and more savory flavor (brand claim, Red Boat). In the Taiwan survey, Vietnamese fish sauces had the highest total nitrogen (Huang et al.).
- Sodium: it varies a lot. Measured sodium ranged from about 5,000 to 12,600 mg per 100 mL, and nearly 40% of products – especially Thai and Korean ones – had more than their labels allowed for (Huang et al., 2025).
Storing Fish Sauce
Unopened, fish sauce keeps for a long time; one maker prints a best-by date three years from production, recommends using an opened bottle within a year, and says refrigeration keeps it freshest but room temperature won’t harm it (brand claim, Red Boat). Salt can crystallize at the bottom of the bottle; that is natural. Keep the cap clean and closed. For other condiments and ferments, see how to store fermented foods.
Cooking With It
Fish sauce is salt and umami in one. Use it where you would use salt – in dressings, marinades, soups, braises and fried rice – and taste as you go: USDA lists about 7,850 mg of sodium per 100 g (USDA), so a tablespoon (18 g) holds roughly 1,400 mg, around 60% of the 2,300 mg Daily Value (FDA). It is at its best balanced with sour (lime), sweet (sugar) and heat (chili), as in Vietnamese nước chấm (recipe card below). Its raw smell softens a lot once it is mixed or cooked.
For a fish-free savory seasoning, fermented soybean products such as soy sauce and miso do a similar job – see our fermented soybean guide.
