What about formaldehyde and other vaccine ingredients?
Here is what the checked sources say. Each title links to the original.
Vaccine Ingredients: Formaldehyde
CHOP explains that formaldehyde is used to inactivate viruses and toxins during manufacturing, and trace amounts can remain: from none to about 0.1 mg per dose, and up to an estimated 0.7 to 0.8 mg in total over the first two years. CHOP says this is considered safe partly because the body makes formaldehyde all the time in normal metabolism: a 2-month-old's blood holds about 1.1 mg at any time, 10 to 220 times more than any single vaccine contains. Reviewed July 2026.
Pharmacokinetic modeling as an approach to assessing the safety of residual formaldehyde in infant vaccines
FDA scientists used a computer model of a 2-month-old to predict what happens to formaldehyde injected with infant vaccines. The model predicted a 200-microgram dose, about what several vaccines at one visit contain, would be essentially gone from the injection site within 30 minutes, with peak blood levels under 1% of the formaldehyde the body already contains. Assuming natural formaldehyde levels cause no harm, the authors concluded residual formaldehyde from infant vaccines continues to be safe.
Common Ingredients in FDA-Approved Vaccines
FDA's overview, current as of March 2026, of what vaccines contain besides the active ingredient: adjuvants such as aluminum salts; stabilizers such as sugars, gelatin and albumin; and antibiotics such as neomycin, used in manufacturing and left in tiny or undetectable amounts. FDA says penicillins, cephalosporins and sulfa drugs are not used, and trace antibiotics have not been clearly linked to severe allergic reactions. On formaldehyde, FDA says the body continuously processes it, and a newborn's body holds 50 to 70 times the most they could receive from a single dose or from vaccines over time.