of the UK government, in order to calm fears that had appeared in the media in a recent period up to that time. Michael Clark of the HPA says published research on mobile phones and masts does not add up to an indictment of WiFi. Effects studied Blood–brain barrier A 2010 review stated that "The balance of experimental evidence does not support an effect of 'non-thermal' radio frequency fields" on the permeability of the blood–brain barrier, but noted that research on low frequency effects and effects in humans was sparse. A 2012 study of low-frequency radiation on humans found "no evidence for acute effects of short-term mobile phone radiation on cerebral blood flow". Cancer There is no known way in which radiofrequency radiation (in contrast to ionizing radiation) affects DNA and causes cancer. In 2011 the IARC, a World Health Organization working group, classified mobile phone use as "possibly carcinogenic to humans". The IARC summed up their conclusion with: "The human epidemiological evidence was mixed. Several small early case–control studies were considered to be largely uninformative. A large cohort study showed no increase in risk of relevant tumours, but it lacked information on level of mobile-phone use and there were several potential sources of misclassification of exposure. The bulk of evidence came from reports of the INTERPHONE study, a very large international, multicentre case–control study and a separate large case–control study from Sweden on gliomas and meningiomas of the brain and acoustic neuromas. While affected by selection bias and information bias to varying degrees, these studies showed an association between glioma and acoustic neuroma and mobile-phone use; specifically in people with highest cumulative use of mobile phones, in people who had used mobile phones on the same side of the head as that on which their tumour developed, and in people whose tumour was in the temporal lobe of the brain (the area of the brain that is most exposed to RF radiation when a wireless phone is used at the ear)". The CDC states that no scientific evidence definitively answers whether mobile phone use causes cancer. In a 2018 statement, the US Food and Drug Administration said that "the current safety limits are set to include a 50-fold safety margin from observed effects of radiofrequency energy exposure". On 1 November 2018, the US National Toxicology Program published the final version (after peer review that was performed through March 2018)