You got mildew growing on the inside of your walls. Somehow you must spray bleach between the walls to kill it. You might check under your flooring, also. Hopefully you have a crawlspace or basement.

Keep water in the traps in the bathroom to prevent sewer gas. If you have peeling paint on the walls, that may well be a sign of moisture inside the walls and wet insulation. Remove the plywood and investigate. If you see signs of mold and mildew, you will need to remove the insulation and disinfect wall cavities and let them dry out. Gutters and downspouts should be clear and carrying water away from the foundation. Inspect the crawl space for standing water. Soil around the home should be sloped away from the foundation to carry water away. You should have adequate foundation ventilation with no dead air spaces and a polyethylene moisture barrier covering the soil. If you have moisture problems, you probably also have termites and/or wood boring insects. You might want to consider getting an exterminator to inspect your home. Most give a free inspection. Mold/mildew can be detrimental to your health, resulting in allergies, headaches, respiratory and other health problems.