Human hair is a material considered useless in most societies and therefore is found in the municipal waste streams in almost all cities and towns of the world . In rural areas or areas with low population density, the hair is thrown away in nature where it slowly decomposes over several years, eventually returning the constituent elements, namely, carbon, nitrogen, sulfur, and so forth, to their respective natural cycles. In urban areas or areas with high population density, it often accumulates in large amounts in the solid waste streams and chokes the drainage systems, posing a multifaceted problem. Due to slow degradation, it stays in the dumps/waste streams for long occupying large volumes of space. Over time, leachate from these dumps increases the nitrogen concentration in the water bodies, causing problems of eutrophication. Burning of human hair or the waste piles containing them—a practice observed in many parts of the world—produces foul odor and toxic gases such as ammonia, carbonyl sulphides, hydrogen sulphides, sulphur dioxide, phenols, nitriles, pyrroles, and pyridines . Open dumps of hair generate hair dust which causes discomfort to people near them and, if inhaled in large amounts, can result in several respiratory problems. Oils, sweat, and other organic matter sticking to the hair rot over time and become a source of foul odor and breeding ground for pathogens.
The best way to address such problems is to develop systems which utilize the waste material as a resource. In addition to reducing waste, it contributes to the economy. As a potential material resource, human hair has the advantage that it is completely biodegradable, renewable, and available in every locality.
Interestingly, while the hair is dumped as waste in most places, certain kinds of high quality human hair and its products are also traded internationally at large scales. In 2010, India alone exported ~1 million kg of human hair and its products worth US $238 million, and total global imports were valued at US $1.24 billion . Largely centered on wigs, hair extensions, and so forth, this trade also has been a source of many of the above mentioned environmental and health problems. Due to hair dust and decaying hair, workers of many hair-processing units in India have increased cases of tuberculosis and respiratory tract infections [4, 5]. Improper disposal of hair and other processing waste in many of these units has been a source of pollution and legal conflicts [4, 6]. In one such case of Jwalapuri market in New Delhi, India , the traders used to put the waste hair to fire. Protests and legal efforts by neighbors in 1998 led to relocation of the processing units to villages in outskirts of New Delhi (personal discussions with Malik, I., 2012), but no systemic improvement was attempted in the processing practices. In Eluru district in Andhra Pradesh (India), dumping of large amount of hair waste from the processing units at the banks of a local river led to pollution, health problems, and conflicts, but the authorities could not resolve the issue because they found no way to deal with the hair waste other than to burn or dump it . These examples show that in spite of a large scale economy running around human hair, there had been no systemic thinking about environmentally safe management of the human hair waste.
There is a great need therefore to develop utilization systems for various kinds of human hair waste found in municipal as well as industrial sources. The efficient and environmentally safe utilization of human hair requires identification of appropriate uses and technologies that can be adapted according to the kind of hair waste and the local circumstances of a place. For example, certain communities in China and India have been using human hair to make fertilizers, while certain communities in the USA and Japan have been making ropes from hair for applications in, for example, horse riding (vide infra).
Every material use and technology, however, also has several sociocultural and economic aspects associated with it, which often determine the adaptability of the use or the technology. Developing appropriate utilization for human hair waste in a context therefore requires considering all possible uses and technologies along with their socioeconomic and environmental impacts. While there is a large body of research literature on the biology of human hair growth  and hair care with its sociocultural aspects  and there is some research on technologies using human hair (vide infra), there is very little literature on systematic environmentally safe management of human hair waste.
This paper explores and assesses various uses of human hair from the perspective of expanding its utilization as a resource while addressing the associated solid waste and environmental problems. Historical and current uses of human hair have been reviewed including the mainstream and local/traditional uses as well as technologies that are being developed in various areas of scientific research. This includes the socioeconomic, environmental, and cultural aspects of the trade systems that have developed around some of the large scale uses. Based on this review, problems and gaps in the current human hair utilization are identified and approaches to address these are discussed. For developing human hair “waste” as a resource, various entrepreneurial considerations such as knowledge and skill requirements and potential markets are discussed. Finally, a policy framework is outlined for developing socially just and environmentally safe utilization systems for the human hair waste.