RH – Relative humidity and its significance in the pharmaceutical industry

Humidity: Before discussing RH it’s important to understand humidity. Humidity is otherwise called moisture content or water content. It plays an important place in the weather and the climate we experience.

How does humidity form?

Due to sunlight, water changes from liquid to vapor through evaporation. so, humidity is the amount of water content or moisture in air. The water vapor mixes with the air, resulting in a rise in humidity levels. The humidity levels of the particular area depend on the availability of water resources humidity is higher near beaches and rivers due to more evaporation due to sunlight, so humidity depends on temperature and availability of the water resources.

There are different types of humidity

• Absolute humidity – Gives total moisture content /water vapor present in given volume of air and it does not change with temperature
• Relative humidity – This is expressed as percentage (%). It is the amount of water vapor in air compared  to the maximum amount of water vapor that air can hold at that specific temperature.
• Specific humidity – It is the grams of water vapor per kilogram of air (g/kg).

Relative humidity:  We have discussed what is relative humidity above, now let us see how RH is influenced by temperature and its significance in pharmaceutical industry

Relative humidity changes with temperature. If the temperature increases, the water vapor carrying capacity of the air increases. But if the water vapor content remains unchanged and relative humidity decreases.

If the temperature decreases, the water vapor carrying capacity of air decreases, if the amount of water vapor in air remains constant, then Relative humidity increases as air will be close to saturation.

Significance of RH:

Relative humidity is playing a critical role in pharmaceutical industry as it impacts the product stability, manufacturing process.

1. Importance of RH – moisture sensitive drugs are common nowadays especially tablets, capsules, High relative humidity causes these products to absorb moisture, and they get degraded either physical degradation or chemical.
2. If you want to know about this practically – take a capsule observe it in packed condition at specified temperature it looks good, now take out and expose it to environment, it absorbs moisture over time and softens.
3. To ensure proper drying after granulation, RH needs to be maintained to maintain the stability of the product.
4. Defects like tackiness, uneven coatings during tablet coating are due to high relative humidity.