to human health. Vaccine hesitant people have also voiced strong concerns about the presence of formaldehyde in vaccines. Formaldehyde is used in very small concentrations to inactivate viruses and bacterial toxins used in vaccines. Very small amounts of residual formaldehyde can be present in vaccines but are far below values harmful to human health. The levels present in vaccines are minuscule when compared to naturally occurring levels of formaldehyde in the human body and pose no significant risk of toxicity. The human body continuously produces formaldehyde naturally and contains 50–70 times the greatest amount of formaldehyde present in any vaccine. Furthermore, the human body is capable of breaking down naturally occurring formaldehyde as well as the small amount of formaldehyde present in vaccines. There is no evidence linking the infrequent exposures to small quantities of formaldehyde present in vaccines with cancer. Sudden infant death syndrome Sudden infant death syndrome (SIDS) is most common in infants around the time in life when they receive many vaccinations. Since the cause of SIDS has not been fully determined, this led to concerns about whether vaccines, in particular diphtheria-tetanus toxoid vaccines, were a possible causal factor. Several studies investigated this and found no evidence supporting a causal link between vaccination and SIDS. In 2003, the Institute of Medicine favored rejection of a causal link to DTwP vaccination and SIDS after reviewing the available evidence. Additional analyses of VAERS data also showed no relationship between vaccination and SIDS. Studies have shown a negative correlation between SIDs and vaccination. That is vaccinated children are less likely to die but no causal link has been found. One suggestion is that infants who are less likely to develop SIDS are more likely to be presented for vaccination. Anthrax vaccines In the mid-1990s media reports on vaccines discussed the Gulf War Syndrome, a multi-symptomatic disorder affecting returning US military veterans of the 1990–1991 Persian Gulf War. Among the first articles of the online magazine Slate was one by Atul Gawande in which the required immunizations received by soldiers, including an anthrax vaccination, were named as one of the likely culprits for the symptoms associated with the Gulf War Syndrome. In the late 1990s Slate published an article on the "brewing rebellion" in the military against anthrax immunization because of "the availability to soldiers of vaccine misinformation on the Internet". Slate continued to report on concerns about the required anthrax