What is E400?
A natural thickener extracted from brown seaweed, used to give ice cream, dressings and sauces a smooth, stable texture.
E400 (alginic acid) is a natural polysaccharide extracted from brown seaweed, used as a thickener, stabiliser and gelling agent. It passes through the body largely undigested, similar to dietary fibre, and every major food safety authority has reviewed it with no safety concern identified. Goodnessly rates it Safe.
Download our app to check additives in everyday foods
Read the FAQ →
What is alginic acid?
Alginic acid is a natural polysaccharide extracted from the cell walls of brown seaweed, including kelp and other Laminaria species. It's the substance that gives seaweed its structure and flexibility, and once extracted, it forms a viscous gel when mixed with water. It's part of a small family of related additives (E400–E404) that includes several alginate salts, each derived the same way but with slightly different properties.
What's it used for?
- Thickening and stabilising ice cream so it stays smooth rather than icy
- Preventing separation in salad dressings and sauces
- Gelling agent in jams, marmalades and desserts
- Improving texture in low-fat dairy products
- Used in some medical and dental products, including heartburn treatments and dental impression moulds
Where you'll find 400 on the shelf
Anywhere a product needs a smooth, stable texture without separating.
Is alginic acid safe? What the research says
Alginic acid has one of the cleanest safety profiles of any thickener in this directory. Here's how regulators currently treat it:
| Region | Status | What this means |
|---|---|---|
| AU/NZ Australia & New Zealand (FSANZ) | Permitted, no limit | Permitted at quantum satis (as much as needed for the intended purpose), with no maximum level in most food categories. |
| EU European Union (EFSA) | Permitted, no ADI | Listed as E400. EFSA's 2017 re-evaluation of the whole alginate family (E400–E404) confirmed no safety concern at typical use levels, with no numerical Acceptable Daily Intake needed. |
| US United States (FDA) | GRAS | Holds Generally Recognized As Safe status for general food use. |
Alginic acid isn't absorbed in the digestive tract and is excreted largely unchanged, similar to dietary fibre. At very high intakes it can bind to some minerals like calcium and reduce their absorption, and it may have a mild laxative effect — neither is a concern at the levels typically found in food. It isn't permitted in most infant formula, though it is allowed in some special weaning foods.
- No significant regulatory changes since 2017: EFSA's group re-evaluation of the alginate family remains the most recent comprehensive review, and no restrictions have followed. Alginic acid isn't currently subject to the kind of re-evaluation debate affecting some newer synthetic additives.
This section is checked periodically rather than continuously — if you're reading this well after the date above, it's worth confirming nothing has changed before citing it.
Who this matters to
- People with a known seaweed or seafood allergy, though genuine allergic reactions to alginic acid itself are rarely documented
- Anyone with a gastrointestinal condition, since alginic acid isn't absorbed by the body and passes through the digestive tract intact
- Otherwise, no population group has a specific safety-based reason to limit E400
Goodnessly rates E400 Safe. It's one of the most extensively reviewed thickeners in the food supply, valued partly because it behaves like a soluble dietary fibre rather than being absorbed and metabolised.
How to spot it on a label
Alginic acid is usually declared clearly. Look out for:
- Alginic acid
- Algin
- 400 or E400
- "Thickener (400)" or "Stabiliser (400)" in the ingredients list
Ice cream, dressings and low-fat dairy products are the most common places to find it.
Related additives
Frequently asked questions
Is E400 the same as algin?
Yes — 400 (or E400) is the additive code for alginic acid, also sometimes called algin. It's a natural polysaccharide extracted from brown seaweed.
Is alginic acid natural?
Yes. Unlike many food additives, alginic acid isn't synthesised in a lab — it's extracted directly from brown seaweed, then purified. No chemical modification is involved.
Is E400 safe for people with a seafood allergy?
Genuine allergic reactions to alginic acid are rarely documented, even though it's derived from seaweed. People with a known seaweed or seafood allergy may still want to exercise some caution and check with a healthcare professional, but it isn't considered a common allergen in the way shellfish protein is.
Does Goodnessly rate E400 as safe, caution, or avoid?
Goodnessly rates E400 (Alginic Acid) as Safe. EFSA's 2017 re-evaluation found no safety concern and no need for a formal daily intake limit, and it's treated by the body much like dietary fibre — passing through undigested rather than being absorbed.
Is E400 vegan and vegetarian?
Yes to both. Alginic acid is extracted entirely from brown seaweed, with no animal-derived ingredients involved.
Don't decode labels by hand
Scan any product with the Goodnessly app to instantly see its full additive breakdown, kept current as new research like this comes to light.
Download our app to check additives in everyday foods
At Goodnessly we aim to educate and empower individuals to make informed choices about everyday products.
© 2026 Goodnessly. All rights reserved.
Facebook
Instagram
X
TikTok