Approximately 90% of the total body burden of absorbed lead is stored directly within human bones and teeth. When lead enters the body through inhalation or ingestion, the skeletal system absorbs it and acts as a primary physiological reservoir, storing the heavy metal safely away from soft tissues for years or even decades. However, during periods of physiological stress, pregnancy, or aging, bone demineralization can release stored lead back into the bloodstream, causing secondary toxicity.