Damp is one of the six climatic pathogenic factors (ie. a quality in the environment or climate which can cause disease). Dampness is the predominant climatic factor in late summer, but also can be encountered in other seasons. Dampness pertains to yin, so it is heavy. An attack by dampness will lead to symptoms such as heaviness of the head , limbs and body. Diseases caused by dampness also have the characteristics of stickiness and stagnation such as lots of sticky phlegm or mucus. They also tend to last a long time and are difficult to treat.