From the Guidelines

Polysorbate 80 is not inherently dangerous, but it can cause allergic reactions in some individuals.

Polysorbate 80 is used in some vaccines, such as the Oxford/Astra-Zeneca and Johnson & Johnson adenoviral vector vaccines, to improve their solubility in water 1.
It can trigger IgE formation in the body, causing mast cell degranulation and leading to allergic reactions, including anaphylaxis 1.
The risk of allergic reactions to polysorbate 80 is relatively low, but it is essential to take a detailed history of previous severe allergic reactions to injectable medications, vaccines, or other allergens, mainly PEG- and polysorbate-containing agents, to help prevent these types of adverse events 1.

Patients who experience severe hypersensitivity reactions (HSRs) to taxanes, which contain polysorbate 80, should not be rechallenged with these drugs 1.
Successful desensitization protocols have been developed for patients who experience HSRs to taxanes 1.
Premedication with corticosteroids and antihistamines is recommended before taxane administration to reduce the risk of HSRs 1.

A history of severe allergic reaction (e.g., anaphylaxis) to polysorbate or any of its components is a contraindication to vaccination with certain COVID-19 vaccines 1.
Immediate allergic reaction of any severity to polysorbate is also a contraindication to vaccination with these vaccines due to the potential for cross-reactive hypersensitivity with the vaccine ingredient polyethylene glycol (PEG) 1.

From the Research

Polysorbate 80 (PS80) is a widely used pharmaceutical excipient that has been implicated in a range of adverse reactions 2.
The composition of PS80 can vary between manufacturers, which may affect its quality and biological impact 2.
Studies have shown that PS80 can cause developmental anomalies, hemolytic toxicity, and target organ toxicity in zebrafish 2.
The primary organs affected by PS80 toxicity include the cardiovascular system, kidneys, intestines, skin, and liver 2.

A 2-year feed study in F344/N rats and B6C3F1 mice found equivocal evidence of carcinogenic activity for PS80 in male rats, but no evidence of carcinogenic activity in female rats or mice 3.
The study also found that PS80 administration was associated with inflammation and squamous hyperplasia of the forestomach in male and female mice, and with ulcers of the forestomach in female mice 3.
Genetic toxicology studies found that PS80 was not mutagenic in Salmonella typhimurium strains 3.

A study found that PS80, along with other dietary emulsifiers, can alter the composition and function of the human gut microbiota, promoting gut inflammation and associated disease states 4.
The study suggested that clinical trials are needed to reduce the usage of detrimental emulsifiers in favor of those with no or low impact on the microbiota 4.

Excessive amounts of PS80 in biotherapeutics have been linked to hypersensitivity and other toxicity-related effects in pediatric patients 5.
A study developed a progressive pediatric safety factor (PPSF) to estimate safe levels of PS80 for young patients, providing an added margin of safety for excipient exposure in sensitive subpopulations 5.

PS80 can interfere with chromatographic analysis, making it difficult to separate from analyte peaks 6.
Sample pretreatment strategies, such as solid-phase extraction and liquid-liquid extraction, can be used to selectively remove PS80 from liquid oral finished drug products 6.