576 JOURNAL OF THE SOCIETY OF COSMETIC CItEMISTS products decrease the level of cystinc cross-links in hair. These include bleaches and especially bleaches followed by permanent waving. Their in- fluence on the dry modulus-and on whatever segment of body is derived from the modulus-is negligible, because the cystinc cross-links are not im- portant load bearing elements in dry fibers within the Hookcan range The toodull of the fibers can be influenced by internal or external deposi- tion of nonreactive materials as well. The resulting systems are composite structures with increased final fiber volumes, therefore, these will be discussed in connection with the fiber diameter effects. A specific case of modulus change occurs when the hair is swollen by liquids which interfere with the internal salt and/or hydrogen bonds of the fibers themselves. Wetting of intact hair by water decreases the modulus by nearly an order of magnitude. The wet modulus of an oxidatively modified hair is even lower. While the modulus reducing effect of fiber swelling liquids must be kept in mind when hair compositions are formulated, the fact in itself is of little importance for the present purpose. Hair body refers primar- ily to the dry and not to the wet state of the hair. The overly high softness of extensively bleached or bleached-waved wet hair may present problems dur- ing a shampoo and wet comb-out, but it does not translate to the dry be- havior. Overall, it may be concluded that present day cosmetic products and processes can influence hair body only marginally through modulus modi- fication. Body modification through fiber diameter increase can be accomplished by internal or external deposition of foreign materials. High levels of internal polymer deposition have been accomplished both on wool and cut hair, with significant increases in body type characteristics. While processes are avail- able for the deposition of solids, mostly polymeric materials, they are not presently utilized in cosmetic products for reasons already mentioned. On the other hand, materials of small molecular weight which are sorbed by the hair -such as alcohols, amines, etc.-most often act as plasticizers, therefore, de- feat the original purpose of increasing body. Only solid materials need to be considered for external deposition which can act as load bearing elements. While setting lotions and gels meet this re- quirement, the approach has serious limitations. The coating thickness must be very limited, if the natural fiber surface and topography are to. be main- tained. Consequently, hair body can be increased by surface deposition only if the coating is continuous and its stiffness is significantly higher than that of the fibers. In this case, the composite material-keratin core and external coating-has high bending stiffness. A specific case is when the solid deposit acts as an adhesive on heavily surface damaged fibrillated fibers. Through adhesively joining these splintered surface units to the main fiber body, they recover their load bearing ability in fiber deformation.

HAIR BODY 577 Based on the above, it can again be concluded that current cosmetic prod- uets do not increase hair body significantly by increasing the diameter of the fibers. Even in the ease of setting gels, the effectiveness is not due primarily to this parameter. Fiber configuration and array represent an area through which hair body is often increased. The higher the curl level and the greater the disorientation of the fibers, the greater will be the bulkiness and, thereby, the body. Perma- nent waving solutions and setting lotions and gels operate by this mechanism. All wet hair treatments can operate through this method, as they provide the opportunity for obtaining a temporary water set in the desired configura- tion. Prior chemical treatments, such as bleaching or waving, which increase the fiber swelling in water improve the water settability further and, therefore, increase the temporary body characteristics. For the sake of completeness, it must be mentioned that some hair care appliances (i.e., curling devices and even hand-held driers) belong to this category. Hand-held driers, in the nor- mal mode of operation, provide water set to the hair at a high angle relative to the skin and reduce the level of eonfigurational conformation among neigh- boring fibers. The factor through which cosmetic products most often influence hair body is the fiber-fiber interaction. No cosmetic treatment leaves the fiber surface unmodified relative to its starting condition. The products which most drastically increase hair body by this mechanism are sprays and polymerie setting lotions. These form rigid joints between con- tacting fibers which are similar to welding in steel structures. In order to over- come the segmental stabilization of involved fibers, the joints must be broken. Even when this is achieved, subsequent fiber displacement is still resisted as long as laterally extending asperities of the broken joints remain on the fibers. Therefore, the structural strength of a sprayed hair mass decreases with comb-out, but does not sink back to its original presprayed level until the residues are fully removed, for instance, by shampooing. The opposite ease-a lowering of body-can be accomplished by surface coating when the deposit is a lubricant with low static frictional eoeffleient. Quaternary ammonium components behave this way. The shear strength of fiber joints is very low in this ease, therefore, the fibers will displace, even under very low external forces and occupy lower-energy positions. With this treatment alone, a bulky high-bodied structure cannot be achieved when all other parameters are equal. Other surface deposited materials can achieve intermediate positions between these extremes. Generalizations, according to conventional classifica- tion of materials, must be avoided. Oil, grease, and wax-type components of shampoos, rinses, and conditioners, which are lubricants in the everyday use of the word, can increase hair body. They form adhesive joints between con- tacting fibers with finite well measurable strength. The bonding strength de-