Moisture can prevent some trichomes from reaching proper temperature for decarboxylation of cannabinoids. This is why smoking wet weed doesn’t get you high. Oxidation of the trichome cuticle (outer waxy shell) is how the oils are somewhat physically protected while other environmental factors like light, humidity and temperature will speed up the degradation process. Terpenes are solvents and will interact with cannabinoids and other compounds in the trichomes over time causing them to break down into other molecules.