Changing the Shape of Hair 180 screening method that also allows measurement of hair damage. Twelve single hair fibers are knotted in a bundle of 4.25 inches in length, then wet wound around a mandrel approximately 6.5–7.0 mm in diameter. The mandrel is then immersed in a capped bottle containing 5–10 mL of the waving lotion. After the specified treatment time, the mandrel is rinsed, immersed in oxidizing agent for 3–5 min and rinsed again. The hair is removed from the mandrel and allowed to assume a circular coil. The “deficiency in tightness,” or DIT, is calculated from the measurements as follows: Eq. 10 A lower DIT value indicates a higher waving efficiency of the lotion. For more details on these test methods, see Wickett and Saviades.23,34 Safety of permanent waving: ATG has a long history of safe consumer use. Allergic reactions to thioglycolate home permanents are extremely rare.64 However, GMT has been reported to cause allergic reactions in hairdressers and in some cases their clients.64-67 GMT is more difficult to rinse from the hair than ATG and residual GMT has been reported on the hair after GMT waving.68,69 Frosch et al. found that among European hairdressers studied 19% were allergic to GMT and only 4% to ATG.70 A report from the Personal Care Products Council’s Chemical Ingredient Review (CIR) on thioglycolates recommends the thioglycolates may be safely used by consumers at infrequent intervals, but recommends that hairdressers avoid skin contact by wearing gloves.71 Hair Straightening/Relaxing Approaches to relaxing/straightening hair: There are two basic approaches to removing the curl from hair. One is to use the permanent waving process in reverse, as it were, to attempt to straighten hair. This is usually referred to simply as straightening.