Hair, whether on the scalp or the body, naturally harbors a diverse community of microorganisms, including bacteria, fungi, and mites. This collection of microbes is part of the larger human microbiome. The hair structure provides a temporary habitat for these organisms, which is facilitated by the hair’s physical characteristics and the biological environment of the scalp.
The Physical Mechanisms of Bacterial Adherence
The hair shaft is not a smooth surface but is covered by overlapping layers of dead cells called the cuticle. These scales are arranged like shingles, creating microscopic ridges and crevices where bacteria can easily lodge and become physically trapped. The hair’s grooved surface contributes to its ability to capture and hold onto environmental particles and microbes.
The scalp is a sebaceous area where glands secrete sebum, an oily substance that coats the hair shaft. Sebum acts as a nutrient-rich film, offering a sticky layer for microbes to attach to and a food source to sustain them.
Bacteria can also form complex structures called biofilms on the hair shaft’s surface, reinforcing their adherence. Specific Gram-negative bacteria, like Pseudomonas aeruginosa and Escherichia coli, colonize the hair shaft, often inhabiting the edges of the cuticle scales.
Sources and Types of Microbes Found in Hair
The microbial community on hair is categorized into resident and transient flora. Resident microbiota live permanently around the hair follicles, forming a stable and mostly harmless population. These organisms include Staphylococcus species (e.g., S. epidermidis), Cutibacterium, and Corynebacterium species.
The hair root and surrounding follicles have a high density of bacteria, suggesting the hair shaft’s microbial community is largely derived from the scalp. The moist, less acidic follicle environment is an ideal niche for organisms like Malassezia fungi.
Transient microbes are picked up temporarily from the external environment, such as through contact with hands, surfaces, or dust. These include various Gram-positive and Gram-negative bacteria, like Pseudomonas aeruginosa and Escherichia coli, which are not typically part of the natural skin flora. Facial hair, such as beards, can collect a high diversity of both resident and transient bacteria due to proximity to the mouth and frequent contact with hands.
Hygiene Practices and Reducing Microbial Load
Managing the microbial load involves establishing a hygiene routine that balances cleanliness with scalp health. Washing frequency should be tailored to the individual based on hair type, sebum production, and activity level.
Washing with shampoo removes dead skin, sweat, product residue, and the excess sebum that feeds the microbial population. Individuals with oily scalps may wash every one to two days, while those with dry, curly, or coily hair may wash less frequently (e.g., once a week) to prevent damage. Periodically using a clarifying shampoo helps remove product buildup that contributes to microbial overgrowth.
Other practices help minimize the spread of transient bacteria. This includes not sharing personal items like combs, brushes, or towels, which can transmit microbes. Covering hair in environments where contamination is a concern, such as food preparation or healthcare settings, acts as a physical barrier against environmental pathogens.