This is a serious potential health problem as well as structual damage. Large quantities of moisture evaporate from the soil and come up through the home. As the moisture moves up through the home, moisture condenses on all cold surfaces. Stop the moisture source by covering the earth in the crawlspace with 6 mil construction plastic out to the walls and overlap the seams. A light cover of gravel to make the pastic lay tightly on the earth is required. You may need addition fresh air ventilation to further dry the air inside the home. Partially opening a couple windows will help short term allowing dry outside air in and wet air out. Mold growth makes most people sick long term. Summer humidity control may require dehumidification. 50% RH during the summer and 30% RH during the winter (no moisture on the windows) is suggested.