Concept of Humidity in Pharmaceutical Industry: Absolute Humidity and Relative Humidity

High humidity causes products to absorb the excess moisture in the air, which can be just as destructive as environments with low humidity. Too much humidity can compromise potency and effectiveness, leading to degradation or even toxicity in some products.

Air humidity is a very important parameter during drug R&D, production, and storage. When we talk about humidity, two definitions are easy to confuse, absolute humidity and relative humidity. What are the relationship and difference between these two measurements of humidity?

What is Absolute Humidity?

• Absolute humidity is a measure of water vapor (moisture) in the air, which means the mass of water vapor per unit volume of gas (grams of moisture per cubic meter of air).
• Absolute Humidity international units is (g/m3). In the pharmaceutical area, absolute humidity is not used too much, as it is difficult to measure the value. And relative humidity is more commonly used during the production and storage of pharmaceutical products.

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What is Relative Humidity?

• The relative humidity is a measure of water vapor (moisture) in the air at a certain temperature compared to what the air can hold at that temperature.
• It is an important index in the pharmaceutical area. Humidity in the warehouse should be 45%～75% in the medicine warehouse. And the relative humidity needs to be controlled well while doing stability research, and during production.

How is Relative Humidity Measured?

• The relative humidity is the percentage of absolute humidity to saturated humidity. The relative humidity of the air in a certain environment can be measured by a hygrometer. At present, there are both dry and wet bulb hygrometers and electronic hygrometers in production.
• Saturated humidity is related to the temperature, so the value of relative humidity is related to the temperature.

Difference between Absolute Humidity and Relative Humidity

The conversion formula for absolute humidity and relative humidity is 

n=(PV)/RT, 

m=18

n=(18PV)/(RT), 

where,

n is absolute humidity 

m is relative humidity.

What is dew point? What is the difference between relative humidity and dew point?

• Relative Humidity and Dew Point are both measures of moisture in the air.
• The dew point is the temperature to which air must be cooled to become saturated with water vapor. The dew point is related to Relative Humidity. The higher the Dew Point temperature, the greater the moisture content of the air.

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