High humidity refers to a high level of water vapor in the air. It is usually measured in terms of relative humidity (RH), which is the amount of water vapor in the air relative to the maximum amount the air can hold at a given temperature. Generally, relative humidity levels above 60% are considered high. At these levels, the air feels heavy, damp, and uncomfortable. High humidity can cause sticky, muggy feelings, and it can make it harder for the body to cool down since sweat evaporates less efficiently. This leads to a hot and clammy sensation and can raise the risk of heat-related illnesses. High humidity also often leads to signs such as condensation on windows, mold growth, and musty smells indoors. It is linked to discomfort, challenges in sleep, and potential health and structural issues. In summary:

• High humidity typically means RH over 60%.
• It causes discomfort, sticky and muggy air.
• It impairs sweat evaporation, making it harder to cool down.
• Can cause mold growth and condensation indoors.
• Often associated with warm and wet weather conditions.

This description of high humidity is consistent across weather and health sources.