Monsoons arrive at the end of AadaanKaala (Uttarayana) a.k.a. Northern solstice and beginning of VisargaKala (Dakshinaayana) a.k.a. Southern solstice. This period weakens our body, diminishes our strength, weakens digestive fire, thus affects the immunity. Rainfall on the heated surface of earth releases the vapours which humidify the air. The resultant humidity creates imbalance of doshas in nature as well as our body. Vata dosha is predominantly vitiated during the rainy season, which creates disparity among pitta and kapha. Thus, change of season demands a change in our routine.