Fetching details from the dictionary...

to get damp; to get moist; to get soggy; to become humid
梅雨の時期は押入れの中が湿気りやすい。
During the rainy season, the inside of closets tends to get damp.
湿気った煎餅は食感が悪くなってしまう。
Rice crackers that have gotten damp lose their crispness.
湿気らないように乾燥剤を入れて保管している。
I store them with a desiccant to prevent moisture buildup.