Dandruff and underarm malodor are caused by microorganisms. Personal hygiene products that contain various types of antimicrobial agents are available and are used for the prevention and alleviation of these conditions. However, their effects are not significant and often do not last long. Working toward a solution, hair was treated with thioglycolic acid, a reducing agent, and then with 2-acryloyloxy ethyl trimethylammonium chloride to covalently bond and immobilize quaternary ammonium chloride QAC to hair shafts. Fourier transform infrared analysis confirmed the bonding of QAC. Time-kill assays were performed to evaluate the antimicrobial activities against two yeast strains responsible for dandruff, two bacterial strains responsible for underarm malodor, and two typical bacterial skin microflora strains. The time-kill assays revealed the antimicrobial effects of QAC against all tested microorganisms. Washing with detergents decreased the antimicrobial effects compared to hair not washed with detergent. This method could potentially replace personal hygiene products, such as shampoos and antiperspirants, which act as antimicrobial agents in the prevention and alleviation of dandruff and underarm malodor.Key words Hair / Antimicrobial activity / Quaternary ammonium chloride / Dandruff / Underarm malodor.
INTRODUCTIONDandruff is a condition in which pieces of dead keratinocytes become visible on the scalp. Dandruff is the most common scalp condition that is often accompanied by itching and erythema Rapini et al., 2007 . The complex causes of dandruff include excess sebum secretion from the sebaceous glands, hormonal imbalance, and excessive proliferation of Malassezia species in the scalp. Malassezia species are yeasts that are found in many environments including the skin, particularly in sebaceous skin areas, such as the scalp, face, and chest. The viable numbers of these yeasts reportedly increase 1.5-2-fold in numbers when dandruff is present Ranganathan and Mukhopadhyay, 2010 . These species degrade triglycerides in the sebum to produce oleic acid, which is absorbed into the stratum corneum. After absorption, oleic acid causes an inflammatory response in keratinocytes, which disrupts homeostasis, leading to the erratic cleavage of keratinocytes, and ultimately to dandruff Dawson, 2006 . Underarm malodor often arises after puberty. In extreme cases, the objectionable malodor can limit normal social activities for the affected person. Humans have two types of sweat glands, namely apocrine and eccrine sweat glands. Underarm malodor is caused by the degradation of secreted milky odorless liquid consisting of electrolytes, steroids, proteins, and lipids from the apocrine glands onto the skin surface by the gram-positive bacteria Corynebacterium xerosis and C. jeikeium, which reside on the skin surface Labows et al., 1979;Leyden et al., 1981;Stefaniak et al., 2010;Noël et al., 2012 . The bacterial biotransformation produces 3-methyl-3-sulfanylhexan-1-ol, 3-sulfanylhexan-1-ol, 3-methyl-3-hydroxy hexanoic acid, 5 -...