Dampness is one of the yin external pathogenic energies. It has a turbid, heavy, and sticky nature and can obstruct the activities of energy transformation performed by the spleen.

There are internal dampness and external dampness, and they cause different symptoms. External dampness refers to the dampness outside the human body, such as on the ground, in the air, or of rain and dew. It may give rise to such symptoms as heavy sensations in the head as if being wrapped up by a wet towel, soreness in the back of the neck, congested chest, sore loins, tired limbs, and sore joints. Internal dampness refers to a stoppage of dampness within the body, normally due to an inability of the spleen to transform dampness because of spleen yang in deficiency. When this occurs, the patient will display such symptoms as poor appetite, diarrhea, abdominal swelling, scant urine, yellowish complexion, edema in the lower limbs, light color of the tongue, and relaxed pulse.