How much humidity is appropriate?

Generally speaking, 40% ~ 60% humidity is the most suitable. If the humidity is too low, the human body will easily feel dry, while if the humidity is too high, it is not suitable. Studies have shown that when the humidity is higher than 65%, the reproduction and reproduction of bacteria will be obviously accelerated. And the amount of hormones secreted by a part of the human body called the pineal gland will also increase.