evidence: Concerns about safety have focused on formaldehyde in part because high concentrations of formaldehyde can damage DNA (the building block of genes) and cause cancerous changes in cells in the laboratory. Although formaldehyde is diluted during the manufacturing process, residual quantities of formaldehyde may be found in several current vaccines (see table below). While formaldehyde is a likely cause of nasopharyngeal cancer, the quantities contained in vaccines are not sufficient to cause cancer. [...] Formaldehyde content of vaccines licensed for use in the United States [...] Not all influenza vaccines contain formaldehyde, but some preparations contain amounts between < 0.005 – 0.1 mg.