j. Cosmet. Sci., 54, 271-281 (May/June 2003) UV radiation: Aggressive agent to the hair--AFM, a new methodology of evaluation V. F. MONTEIRO, A. S. PINHEIRO, E.R. LEITE, J. A.M. AGNELLI, M. A. PEREIRA-DA-SILVA, and E. LONGO, CMDMC/LIEC/DQ/UFSCar (V.F.M., A.S.P., E.L.) and DEMa/UFSCar •.A.M.A.), Universidade Federal de S•7o Carlos, Rod Washington Luis Km 235, Caixa Postal, 676, S•7o Carlos, SP, Brazil 13565-905 and Universidade de S•7o Paulo, Instimto de Fisica, S•o Carlos, SP, Brazil 13560-970 (M.A.P.-D.-S.). Accepted for publication June 18, 2002. Synopsis A new method for morphological hair analysis at high resolution and under ambient conditions is presented in this paper. The AFM has been used in these experiments to analyze morphological changes in hair roughness and thickness after UV radiation. Through the powerful analytical AFM tools, changes in hair morphology can be proven. A new quantitative methodology to evaluate hair structure is presented in this paper. INTRODUCTION Constant investigations into technological development of hair care products that exceed consumers' expectance have long represented a challenge for researchers and scientists. Many investigations have been carried out to develop effective cosmetic products for human hair, and scientists have employed a variety of methods in their attempts to understand the alterations and to prove the cosmetic efficacy of the products. Recent reports on the harmful effects of sunlight on human skin have raised the aware- ness of the deleterious effect of sunlight on biological tissues in general. Hair can also suffer photo degradation (1), which can contribute significantly to overall hair damage (2). The influence of sunlight on untreated human hair has been extensively analyzed by examination of the protein, melanin, and lipid components as well as the morphological areas on irradiated hair (3). These studies have demonstrated that the physical and chemical modifications of hair are marked by intrinsic patterns of damage correlated to its pigmentation and to the amount and intensity of sunlight to which it has been exposed. UV-A and the visible part of sunlight (VIS) damage hair significantly however, hair's properties are also influenced to a minor extent by UV-B and IR irradiation. Black hair is largely protected from damage by the pigment eumelanin. In contrast, blonde 271

272 JOURNAL OF COSMETIC SCIENCE hair is detectably photochemically damaged due to its low pigment content or pigmen- tation with pheomelanin. Hair damage causes a reduction in tensile and fatigue properties (3). According to Robbins and Bahl (4) and Speakman and McMahon (5), the reduction is largely attrib- uted to chemical damage to the protein chains, especially the S-S covalent crosslinks in cystine. They have found that photochemical damage, the loss of crosslinks, leads to an increase in solvent swelling, a finding not shared by Wolfram (6), who argues that crosslinking between amino acid residues is induced by irradiation and that these new crosslinks would limit the solvent swelling in the case of keratin fibers. According to the hair photolysis mechanism proposed by Tolgyesi (1), cystine, tyrosine, phenylalanine, and tryptophan residues absorb UV radiation, resulting in the formation of free radicals. Homolytic scission of disulfide bonds occurs. Melanin, the natural coloring matter in hair, provides partial protection to the hair fiber. It acts in a sacrificial manner, resulting in lightening of hair color. Tolgyesi explained that melanin, by its comprehensive system of double bonds and conjugated carbonyl groups, protects hair by scavenging free radicals generated by exposure to light. Wei (7) furthered the concept of the free-radical mechanism, showing that, all other factors being equal, the extent of photodamage is proportional to the square root of the amount of free-radical initiators present in the fiber. The mechanism assumes that the S-S group is the initiator, giving two -S free radicals by homolytic scission. A study using field emission scanning electron microscopy (FESEM) was carried out by Ruetsch et aL (8) to monitor the effects of UV irradiation on the physical nature of hair fibers. Long-term UV irradiation-humidification cycling causes thinning and fusion of the surface cuticle cell, as well as fusion of the cuticular sheath into a solid, rigid, and brittle unit. Swift and Smith (9) reported the advantages of the use of AFM, such as the greater details in the hair's cuticular surfaces that appear not to be as smooth as had been previously supposed when evaluated by SEM. They observed that the surface of the hair gradually changes as a function of its length, measured from the hair root. This tech- nique and the effects of subsequent damage are herein discussed. The study reported in this paper verified these initial findings on the damage of human hair exposed to sunlight, and also determined the photochemical damages associated with the physical morphological changes in hair structure. Scanning electronic micros- copy (SEM) analyzed the damage of UV radiation on hair fibers. This technique was employed to observe the damage induced on hair fibers by UV radiation. The use of atomic force microscopy (AFM) provides a new understanding of the mechanism of UV radiation damage to hair by physical quantification of the nature and damage of hair cuticle as roughness and thinning. MATERIALS AND METHODS MATERIALS Untreated black Caucasian hair was obtained from De Meo Bros., New York. Hair samples were pre-treated using 3% LAS (lauryl ammonium sulfate).