While there's no set humidity threshold above which general comfort level begins to deteriorate, NOAA typically considers relative humidity (RH) levels of 50% or more, and dewpoints (a more direct measure of humidity) above 65 F (18 C) to be uncomfortably high.

However, the National Oceanic and Atmospheric Administration considers relative humidity levels of 50 percent or more and dewpoints (a direct measure of relative humidity) above 65 F to be high and uncomfortably.

While comfort levels are subjective, the National Weather Service states that dew points between 55 and 65 become “sticky and muggy” and dew points above 65 become highly uncomfortable and oppressive. A quick rule of thumb is that the closer the dew point is to the temperature of the air, the more likely the air will feel humid.

According to the Environmental Protection Agency, indoor relative humidity should be kept below 60%. Ideally, between 30% and 50%. The DOH states that “for thermal comfort, the optimum range for relative humidity is 40 to 60 percent in the summer and 30 to 50 percent in the winter.”