Barometric pressure, commonly known as atmospheric pressure, describes the amount of weight being exerted by air onto the Earth. To determine what the barometric pressure is, a barometer is used to measure the air pressure in a given area. For some, changes in the barometric pressure can increase arthritic pain, headaches and sinus pain, according to MedicineNet.com.

Weather patterns are a common cause in barometric pressure drops. When low-pressure weather systems move in over a certain area, not only is pressure in the atmosphere shifted, but it causes the barometric pressure reading to drop. A low-pressure system indicates that low-pressure air rises and begins to cool. Once the low-pressure air has risen into the atmosphere, it creates condensation and causes it to rain, snow or create ice. MedicineNet explains that the weather shifting through the atmosphere can cause those who suffer from arthritis to feel more joint pain, because low barometric pressure is associated with storms and bad weather.

Most areas on Earth are considered to be low altitude. As you go up in elevation, whether it be hiking to the top of a mountain or living in a city like Denver, which is a mile above sea level, the barometric air pressure drops. Air contains less pressure the higher altitude you go, which causes some to experience altitude sickness. Just as a low-pressure system causes the barometric pressure drop to cause pain in some, going high into air that has little pressure causes dizziness, nausea, fatigue or headache, according to MedlinePlus.

Humidity refers to the amount of moisture in the air, and when there are higher levels of vapor in the air we breathe, it can decrease the amount of barometric, or air pressure in the atmosphere. Relative humidity refers to the moisture in the air, measured in percentages. With the inclusion of vapor into the air, it takes over some of the pressure. Those who live in humid climates where the barometric pressure drops may be prone to migraine headaches, because the oxygen levels change with varying pressure. According to a 1981 study by Dr. Galina Mindlin with the Jefferson Medical College in Philadelphia, it was discovered that migraine headache levels increased during low-pressure or humidity--both of which cause the barometric pressure to drop.