What is paralytic shellfish poisoning? Symptoms and limits
Paralytic shellfish poisoning comes from saxitoxins in shellfish. See its symptoms, how it differs from ASP, DSP and NSP, and the GB, NI and US PSP limits.
What is paralytic shellfish poisoning?
Paralytic shellfish poisoning (PSP) is caused by eating shellfish contaminated with saxitoxins. Dinoflagellates, a type of marine algae, produce them. Cooking or freezing does not make contaminated shellfish safe. Clams and mussels are common sources, and severe cases can cause respiratory failure, according to the CDC Yellow Book.
What causes paralytic shellfish poisoning
Shellfish become contaminated with saxitoxins produced by marine algae. Cooking and freezing don't destroy these toxins. The CDC also lists canning, pickling, salting, or smoking as methods that do not destroy them.
Paralytic shellfish poisoning symptoms
Symptoms often start within 30 to 60 minutes of eating. CDC also records a wider window, from 30 minutes to four hours. The first signs are tingling or numbness of the face, lips, tongue and limbs. Nausea, vomiting, diarrhea and headache can follow. In severe illness, people can have difficulty swallowing, paralysis and respiratory failure (CDC).
Anyone who may have PSP needs medical advice at once, because breathing can fail. In the UK, the NHS says to call 999 for severe symptoms such as trouble breathing. In the US, the CDC lists Poison Control at 1-800-222-1222. Call emergency services first if breathing is affected.
PSP, ASP, DSP and NSP compared
"Shellfish poisoning" covers more than PSP. The CDC separates the four main marine biotoxin types like this:
| Syndrome | Toxin | Typical effects |
|---|---|---|
| Paralytic (PSP) | Saxitoxins | Tingling and numbness; paralysis and respiratory failure in severe cases |
| Amnesic (ASP) | Domoic acid | Gastrointestinal illness; cognitive impairment and memory loss can follow |
| Diarrhetic (DSP) | Toxins including okadaic acid | Diarrhea, abdominal pain, nausea and vomiting |
| Neurotoxic (NSP) | Brevetoxins | Gastrointestinal and neurological symptoms |
Source: CDC Yellow Book.
Legal limits for PSP and other shellfish toxins
Great Britain
In Great Britain, assimilated Regulation (EC) 853/2004, Annex III, Section VII sets the maximum total marine biotoxins, measured in the whole body or any part edible separately.
| Toxin group | GB maximum |
|---|---|
| PSP | 800 micrograms/kg |
| ASP | 20 mg domoic acid/kg |
| Okadaic acid, dinophysistoxins and pectenotoxins together | 160 micrograms okadaic-acid equivalents/kg |
| Yessotoxins | 3.75 mg yessotoxin equivalents/kg |
| Azaspiracids | 160 micrograms azaspiracid equivalents/kg |
Northern Ireland and the EU
Northern Ireland follows EU food law under the Windsor Framework, as the FSA confirms. The EU text differs on two rows. Delegated Regulation (EU) 2021/1374, in force since 9 September 2021, expressed the PSP limit as 800 micrograms of saxitoxin equivalents diHCl/kg. It also took pectenotoxins out of the combined okadaic acid limit, which now covers okadaic acid and dinophysistoxins only. The May 2026 consolidated text still reads this way. That change is not in the GB assimilated text, so one UK-wide limits table will misstate either Great Britain or Northern Ireland.
United States
The FDA's PSP compliance policy gives an enforcement criterion, not a statutory maximum. Under CPG Sec. 540.250, a lot of clams, mussels or oysters is actionable if one subsample has 80 micrograms or more of PSP per 100 g of meat. The policy names the assay to use. That converts to 800 micrograms/kg, the same mass figure as the GB rule. FDA says "or more", while the GB rule says the total must not exceed 800 micrograms/kg.
How harvesting areas are monitored
The FSA describes phytoplankton and biotoxin monitoring for England, Wales and Northern Ireland. Phytoplankton monitoring gives early warning of toxic events, and affected areas are closed for harvesting when toxins exceed legal limits. Food businesses remain responsible for meeting those limits, the FSA says. Food Standards Scotland monitors phytoplankton and shellfish flesh in Scotland and issues a temporary closure notice after a breach. A sampling schedule shows when an area is tested, not that today's harvest is safe. An open area isn't a guarantee that a batch complies. Class A, B or C classification does not establish compliance with toxin limits. Purification rules in the same annex address sewage contamination.
You can explore the official sources in RegAffairs AI's answer on shellfish poisoning and toxin limits.