Human hair does decompose, but its breakdown is a gradual process influenced by various environmental conditions. Its surprising durability stems from its unique structural makeup, making it one of the more persistent biological materials found in nature.
Hair’s Unique Composition
Hair is primarily composed of keratin, a fibrous structural protein that accounts for about 95% of its mass. This protein is remarkably tough and insoluble due to the tightly packed arrangement of its amino acids and numerous disulfide bonds. These strong chemical linkages create a rigid and stable matrix, providing hair with its inherent strength and resilience, making it resistant to decomposition.
Factors Influencing Decomposition
Moisture is a primary determinant; wet or damp conditions support microbial activity necessary for breakdown. Hair is not highly porous and does not absorb water easily, contributing to its slow decomposition. Conversely, extremely dry environments can preserve hair for millennia by inhibiting microbial growth.
Temperature also plays a role; moderate warmth accelerates microbial activity, while extreme cold halts it, leading to preservation. High temperatures can denature the keratin protein, weakening the hair structure. Oxygen availability is another important factor; aerobic conditions, such as those in a well-aerated compost pile, promote faster decomposition. In contrast, low-oxygen or anaerobic environments significantly slow the process.
The pH level of the surrounding environment affects hair structure and microorganism activity. Hair is naturally slightly acidic (pH 4.5-5.5). Extreme pH, either highly acidic or alkaline, can damage the hair’s cuticle and disrupt its protein structure, making it more susceptible to breakdown. Strong alkaline solutions, for example, can dissolve hair quickly. The presence of active microorganisms like bacteria and fungi, particularly those capable of degrading keratin, is essential for decomposition.
Decomposition Durations
The time hair takes to decompose varies widely depending on environmental conditions. In typical environments, such as buried in soil, human hair can take one to two years to fully break down. Under moist conditions or within a healthy compost pile, decomposition can occur more rapidly, sometimes within a few weeks to several months. Hair can endure for surprisingly long periods in dry environments, lasting for millennia. This persistence is evident in archaeological finds, where hair has been observed on human remains over 100 years old, and even on mummies thousands of years old.
The Breakdown Process
Hair decomposition primarily involves biological and chemical processes mediated by microorganisms. Bacteria and fungi are the main agents, producing specialized enzymes known as keratinases. Keratinases cleave the tough peptide and disulfide bonds within the keratin protein structure. This enzymatic action initiates a slow, gradual process of hydrolysis and oxidation, breaking down the complex keratin into simpler compounds. The sequential steps involve the denaturation of keratin, followed by hydrolysis into smaller peptides and amino acids, and finally, transamination.