instead of curling it. The same chemical methods can be used for this, but the hair is not wrapped around rods. Other modern perms Other types of modern perms include exothermic perms, which are self timing and self heating; and neutral, or low pH, thioglycolate free perms. Digital perms were introduced in the 21st century and in use especially in modern Asian cultures. The process was patented and invented by a Japanese company, Paimore Ltd. Technical considerations There are two parts to a perm: the physical action of wrapping the hair, and the chemical phase. Both of these can affect the result. Important physical variables involved are what type of rod is used, how the hair is wrapped and how end papers are used. The two most common types of rods are straight and concave; each giving a different curl effect. The wrapping method is either spiral or croquinole, and various types and the positioning of end papers can be used with any combination of the above. Generally, smaller rods will produce smaller, tighter curls and increase the appearance of shortening the hair. The chemical solution used in the perming process is determined by the client's hair type and the pH of the solution. Classic alkaline perms are used for stronger, coarser hair. They work at room temperature and usually contain ammonium thioglycolate in the pH range of 9-10. Acid perms are used on more delicate or thinner hair. They require outside heat application and usually contain glyceryl monothioglycolate (GMT) in the pH range of 6.5-8.2. Glyceryl Monothioglycolate is considered a recent innovation in perming technology due to its high curling power near the pH of hair. This allows hair cuticles to remain closed during the perming process, minimizing damage to the hair structure. Safety considerations A poorly performed permanent wave will result in breakage of the disulfide bonds through chemical reduction, because it fails to fix the newly formed bonds. This results in hair that is no longer elastic and flexible, but brittle and fragile. At this point, even combing the hair will result in hair loss. The hair shafts will experience fracture where they exit the scalp. Because the bulb of hair has not been removed, though, the hair follicle is not damaged and the hair will regrow. Home perms A number of brands of home permanent kits were available since the invention of the 'cold wave' in