The NOAEL is the lowest "dose" or exposure level to a non-cancer-causing chemical at which no increase in adverse effects is seen in test animals compared with animals in a control group. First, a NOAEL is determined. For instance, it is established that no adverse effects are seen in test animals after they have been exposed to a set amount, such as an ounce per day for a year, whereas a higher exposure causes adverse effects. Then this level is divided by one or more uncertainty factors to establish an acceptable human exposure level. Regulatory agencies typically use a factor of 10, 100, or 1,000 to account for the uncertainty arising from the fact that the NOAEL is based on an animal study but is being extrapolated to set a "safe" level of exposure for human beings.