Dirt and dust collect on walls and ceilings around vents where heated and cooled air exits. This is normal but if you also see dark shadows around windows or on the edge of carpet near walls it signals air leaks and caulking is in order to seal them up. Depending on the individual mold can be an aesthetic problem or a serious health issue. To clear it up start by getting humidity under control, then tackle surface mold with a mild solution of household bleach in warm water. Purchase fixtures designed for direct contact with insulation.
Airtight fixtures are also available.
Apply a generous coat of petroleum jelly on all skin surfaces to keep minute fiberglass particles out of pores. Then cover as much skin as you can. There is a temporary but quick fix for faucets with a slow leak. A box in the fridge captures bad odors, in the freezer too. Eats pet odors on carpets too.