Specific Absorption Rate (SAR) measures the rate at which RF energy is absorbed by body tissue, expressed in watts per kilogram (W/kg). SAR is used to rate cell phones and other devices held against the body. The FCC limit for cell phones is 1.6 W/kg averaged over 1 gram of tissue.
Based on Building Biology Institute guidelines (W/kg (watts per kilogram)):
See where common exposures fall on the scale:
Showing 871 studies with measured sar (specific absorption rate) exposure
Conover DL et al. · 1992
Workers operating industrial dielectric heaters showed dangerously high electromagnetic energy absorption in their ankles. Twenty-seven percent of these heating machines created electrical currents through workers' feet exceeding safety limits, with maximum energy absorption reaching 176 watts per kilogram in ankle tissue.
Lu ST et al. · 2010
Researchers exposed four rhesus monkeys to intense 2.8 GHz microwave radiation for 36 hours total over three weeks and measured any damage to the corneal endothelium (the inner layer of cells in the eye's cornea). The study found no changes in corneal cell density or thickness, even at power levels more than ten times higher than previous studies that reported eye damage. This suggests that microwave exposure at these levels may not harm this specific part of the eye.
Liu YX et al. · 2012
Researchers exposed rat brain support cells to cell phone radiation at 1950 MHz for 48 hours. The radiation damaged cellular powerhouses and triggered cell death through a specific pathway, though it didn't promote tumors. This suggests prolonged exposure may harm healthy brain cells.
Park J, Kwon JH, Kim N, Song K · 2017
Researchers exposed brain cells to cell phone radiation (1950 MHz) for 2 hours daily over 3 days to see if it affected amyloid-beta processing, which is linked to Alzheimer's disease. They found no significant changes in the proteins that create these brain plaques. However, the researchers noted that longer-term exposure might produce different results than their short 3-day study.
Bouji M, Lecomte A, Gamez C, Blazy K, Villégier AS. · 2016
Researchers exposed both young and elderly rats to cell phone radiation (900 MHz) for 45 minutes daily over one month to see if aging brains were more vulnerable to EMF effects. The study found that while elderly rats showed expected age-related brain problems, the radiation exposure didn't make these problems worse. Interestingly, both young and old rats exposed to radiation showed reduced anxiety-like behaviors.
Yang XS, He GL, Hao YT, Xiao Y, Chen CH, Zhang GB, Yu ZP. · 2012
Researchers exposed rats to 2.45 GHz electromagnetic fields (the same frequency as WiFi and microwave ovens) and found that their brain cells produced stress proteins in response. The hippocampus, a brain region crucial for memory and learning, showed increased levels of heat shock proteins (HSP27 and HSP70), which cells produce when they're under stress. This provides direct biological evidence that EMF exposure triggers a stress response in brain tissue.
Yang XS, He GL, Hao YT, Xiao Y, Chen CH, Zhang GB, Yu ZP. · 2012
Researchers exposed rats to WiFi-frequency radiation (2.45 GHz) for 20 minutes and found it triggered stress responses in brain cells. The radiation caused neurons in the hippocampus to produce heat shock proteins, indicating cellular damage in the brain region responsible for memory and learning.
Bouji M, Lecomte A, Hode Y, de Seze R, Villégier AS. · 2012
French researchers exposed young and middle-aged rats to cell phone radiation (900 MHz) for 15 minutes to study brain effects. They found that older rats showed increased brain inflammation and enhanced emotional memory, while younger rats had elevated stress hormones. The study reveals that age significantly affects how the brain responds to radiofrequency radiation.
Bouji M, Lecomte A, Hode Y, de Seze R, Villégier AS · 2012
French researchers exposed young and middle-aged rats to 15 minutes of cell phone radiation (900 MHz) at high levels to study brain and stress responses. They found that middle-aged rats showed increased brain inflammation and enhanced emotional memory, while young rats had elevated stress hormone levels. The study reveals that age affects how the brain responds to radiofrequency exposure, with different vulnerabilities at different life stages.
Ammari M et al. · 2010
French researchers exposed rats to cell phone radiation for 8 weeks and found increased brain inflammation markers that lasted at least 10 days after exposure ended. This suggests chronic mobile phone use may trigger inflammatory brain responses similar to those seen in neurodegenerative diseases.
Yang X, He G, Hao Y, Chen C, Li M, Wang Y, Zhang G, Yu Z · 2010
Researchers exposed brain immune cells called microglia to 2.45 GHz radiofrequency radiation (the same frequency used in WiFi and microwave ovens) for 20 minutes at high intensity. They found that this EMF exposure triggered inflammation in the brain cells by activating a specific molecular pathway called JAK2-STAT3, which led to increased production of inflammatory chemicals. This suggests that EMF exposure may contribute to brain inflammation through well-defined biological mechanisms.
Ammari M, Lecomte A, Sakly M, Abdelmelek H, de-Seze R. · 2008
French researchers exposed rats to cell phone radiation and measured brain enzyme activity. High-intensity exposure (6 W/kg) for 15 minutes daily reduced brain activity in memory and decision-making regions after one week. Lower exposures showed no effects, suggesting intensity matters for brain function.
Ammari M et al. · 2008
French researchers exposed rats to cell phone radiation (900 MHz) for 24 weeks and found that high-level exposure caused persistent brain inflammation. The study measured GFAP, a protein that increases when brain support cells called astrocytes become activated in response to injury or stress. This suggests that chronic cell phone radiation exposure may trigger ongoing inflammatory responses in brain tissue.
Ammari M et al. · 2008
French researchers exposed rats to 900-MHz cell phone radiation for up to 24 weeks to test whether it would impair their spatial memory and navigation abilities. The rats showed no memory deficits even when exposed to radiation levels 3-12 times higher than typical cell phone use. This suggests that chronic exposure to GSM cell phone signals may not directly damage the brain's memory systems.
Brillaud E, Piotrowski A, de Seze R. · 2007
French researchers exposed rats to cell phone radiation (900MHz GSM signal) for just 15 minutes and then examined their brains over the following 10 days. They found significant increases in glial cell activity (brain cells that support and protect neurons) in multiple brain regions, peaking 2-3 days after exposure. This glial response indicates the brain was reacting to the radiation exposure as if responding to injury or stress.
Brillaud E, Piotrowski A, de Seze R · 2007
French researchers exposed rats to 15 minutes of cell phone radiation and found brain inflammation that peaked after 2 days and lasted up to 10 days. The study measured stress proteins in brain tissue, suggesting brief phone exposure can trigger inflammatory responses in the brain.
Mausset-Bonnefont AL et al. · 2004
French researchers exposed rats to cell phone radiation (900 MHz GSM) for just 15 minutes and found immediate brain damage. The exposure triggered a strong inflammatory response from brain support cells (glial reaction) and disrupted key brain chemical systems involved in movement, memory, and mood. Despite these cellular changes, the rats showed no obvious behavioral problems in the short term.
Adair ER, Cobb BL, Mylacraine KS, Kelleher SA, · 1999
Researchers exposed 14 volunteers to radio frequency radiation at 450 and 2450 MHz (similar to cell phone frequencies) for 45 minutes at power levels exceeding current safety guidelines. The exposure caused measurable increases in skin temperature, with the body responding through increased sweating and blood flow to maintain normal core body temperature within 0.1 degrees Celsius.
Behari J, Kunjilwar KK, and Pyne S · 1998
Researchers exposed developing rats to radiofrequency radiation similar to what cell phones emit and found it significantly increased activity of a critical brain enzyme called Na+-K+-ATPase by 15-20%. This enzyme is essential for nerve cell function and brain development. The findings suggest that RF radiation can alter fundamental brain chemistry in developing animals, raising concerns about potential effects on brain development in children.
Hao Y, Yang X, Chen C, Yuan-Wang, Wang X, Li M, Yu Z · 2010
Researchers exposed brain immune cells called microglia to 2.45 GHz radiation (the same frequency used in WiFi and microwave ovens) for 20 minutes and found it activated these cells through a specific cellular pathway called STAT3. The activated microglia began producing inflammatory molecules including nitric oxide and tumor necrosis factor-alpha. This matters because microglial activation is linked to brain inflammation and neurological problems.
Maes A, Collier M, Verschaeve L · 2000
Belgian researchers exposed human immune cells (lymphocytes) to radiation from a 455.7 MHz car phone at high intensity levels (6.5 W/kg SAR) to see if it would cause genetic damage or make the cells more vulnerable to other cancer-causing agents. They found no evidence that the phone radiation caused chromosome damage on its own, nor did it increase the harmful effects when combined with known mutagens like chemicals or X-rays.
Harvey C, French PW. · 2000
Researchers exposed human immune cells (mast cells) to microwave radiation at 864.3 MHz for 20 minutes daily over a week, using power levels that kept the cells cooler than body temperature. They found that this non-thermal exposure altered the activity of protein kinase C (a key cellular signaling molecule) and changed the expression of three genes, including one linked to cancer development and another associated with cell death.
Harvey C, French PW · 2000
Researchers exposed human immune cells to microwave radiation at 864.3 MHz for 20 minutes daily over seven days. The exposure altered key cellular proteins and changed gene expression related to cell growth and death, even at temperatures too low to cause heating effects.
Natarajan M, Vijayalaxmi , Szilagyi M, Roldan FN, Meltz ML · 2002
Researchers exposed human immune cells called monocytes to high-powered pulsed microwave radiation at 8.2 GHz for 90 minutes and measured changes in their cellular activity. They found that the radiation triggered a 3.6-fold increase in the activity of NF-κB, a crucial protein that controls genes involved in inflammation, immune responses, and cell survival. This demonstrates that microwave radiation can activate important cellular signaling pathways that regulate long-term cellular functions.
Kim TH et al. · 2008
Researchers exposed mice to cell phone radiation at 849 MHz and 1763 MHz frequencies for up to 12 months, using radiation levels about 4 times higher than current safety limits. They found no changes in brain cell death, cell growth, or tissue damage compared to unexposed mice. This suggests that chronic exposure to these specific frequencies at high levels may not cause detectable brain tissue changes in mice.