The ideal indoor humidity level is either 35% to 45% or 40% to 50% depending on who you ask. Thankfully, the human body is quite flexible and you do not have too aim at an exact figure. The important thing is to avoid extremes. Living indoors is not entirely natural. The artificial environments that we create for ourselves can sometimes cause extremes of humidity to occur. For short periods of time this is nothing to worry about, but the long term effects can be quite unpleasant.
If the humidity level regularly exceeds 50% you are likely to experience a rapidly increasing dust mite population, which will affect allergy sufferers. Permanently damp rooms tend to have a musty smell. The damp air is a perfect breeding ground for mold, mildew and fungus, which can cause serious health problems. Where ever possible the cause of such conditions should be removed, but it is not always that simple and a dehumidifier may be required. A modern dehumidifier with built in humidistat can be programmed to maintain a humidity level below 50%. There are a wide variety available, so it is important to find the correct type for your situation. A useful guide to dehumidifiers can be found at DehumidifierTips.com
Consistently low humidity levels are also bad. This tends to occur when the weather is cold outside and we turn up the heat in our homes. The most noticeable effects are a sore throat and sinus pain, symptoms that are common in modern society at certain times of year. You can also get dry skin and itchy eyes. The solution is to buy a humidifier that will put moisture back into the air. Like dehumidifiers, these can be programmed to operate automatically, and there is a huge range available that make the most of a variety of different humidification techniques. These techniques are explored in detail at HumidifierInformation.com together with everything else you need to know on the subject.
If any of these symptoms sound familiar, maybe you should buy a hygrometer (humidity meter) and take some readings to find out if humidity is the cause. With modern technology at your disposal there is no need for your health to suffer.