Humidity has physical and chemical effects on products. Temperature and humidity variations can trigger condensation. Some typical problems that can result from exposure to a warm, humid environment are:

Surface Effects
Oxidation and/or galvanic corrosion of metals.
Increased chemical reactions.
Chemical or electrochemical breakdown of organic and inorganic surface coatings.
Interaction of surface moisture with deposits from external sources to produce a corrosive film.
Changes in friction coefficients, resulting in binding or sticking.
Changes in Material Properties
Swelling of materials due to sorption effects.
Loss of physical strength.
Changes in electrical and thermal insulating characteristics.
Delamination of composite materials.
Change in elasticity or plasticity.
Degradation of hygroscopic materials.
Degradation of explosives and propellants by absorption.
Degradation of optical element image transmission quality.
Degradation of lubricants.
Condensation and Free Water
Electrical short circuits.
Fogging of optical surfaces.
Changes in thermal transfer characteristics.
Typical Test Specifications
MIL-STD-202	ASTM
MIL-STD-810	BELLCORE GR-63-CORE
MIL-STD-883	IEC 68
MIL-E-5272	RTCA DO-160
MIL-T-5422	SAE
MIL-PRF-28800