But for some materials, each cycle causes tiny fractures to grow. Deterioration increases as cracks are opened further. Research on painting deterioration by Stefan Michalski suggests that this may be a cause of surface cracks. The amount of mechanical damage is directly related to the type of material, the constraint on the material and amount of RH change. Small changes cause small effects.
Big changes cause big effects.
If tension climbs in a constrained material it eventually reaches a breaking point. For example, wood needs room to expand and contract when RH fluctuates. If a wood panel is nailed into a frame it will split. If it is placed in a groove, without glue, with space for expansion and contraction, it probably will not crack. The Canadian Conservation Institute, looking at wood artifacts and painted panels, divided materials into four levels of vulnerability to RH changes.