PERSORPTION 121 Boric acid powders, solutions and ointments have been investigated but no persorption could be detected through normal skin, as determined by an increase of boron content in blood by chemical assay (30). The passage of cortisone through the skin of adrenalectomized mice has been measured by the eosinopenic response (31). Most vitamins have been found to pene- trate the skin enough to relieve the various deficiency symptoms in rats when vigorous application and special ointments are used (32). With human skin, similar activities (33) have been reported and in one instance actual recovery of vitamin B-6 in the urine has been recorded (34). Nico- tinic acid derivatives, used for peripheral vasodilation when applied locally, have been found to raise the blood level of the vitamin (35). Tetraethyl- pyrophosphate certainly passed through the skin when it almost caused the death of a child by its blocking action on the heart (36). In a high con- centration, DDT exhibits toxicity when placed in contact with the skin especially when chlorinated solvents are present (37). Of the war gases, the mustard type at low concentration appears to penetrate uniformly through the epidermal barrier, whereas lewisite has been found more in the cellular lining of the hair follicles. Both have much less effect in cold weather (38). Local anesthetic action is also a unique but valuable way of observing the passage of compounds through the skin (39). A polyethylene glycol ointment base permits the dye, phenolsulfonphthalein, to pass through the skin much better than a petrolatum base (40). Radioactive tracers are now being used to determine the amounts and the pathways of persorption. Mercuric chloride with radioactive mercury has been found to have no penetrative ability (41). On the other hand C TM hydrocortisone was easily followed through the skin and into the blood system by autoradiography (42). Sodium retention has also been meas- ured following the application of fluorohydrocortisone lotion (43). Hair growth has been inhibited in rats by application of both cortisone and es- trogens (44) but this does not necessarily indicate that persorption has taken place. However, in other tests, it was found that the sex hormones exhibited their respective actions on the rat, estradiol being catabolic and methyl testosterone anabolic (45). With humans, it has been reported that an estrogen lotion applied to male scalps has reduced the amount of falling hair (46). These examples could possibly involve persorption. When the applied material has passed through the epidermal barrier its continued movement largely depends on the vascularity and circulation in the underlying tissues (47). This has been increased by the use of periph- eral vascular dilators such as salicylic acid, nicotinic acid, benzedrine and their derivatives (48). Some of these may be administered orally or by inunction. Benzyl nicotinate has been shown to increase the rapidity with which S :•5 may be excreted in the urine following inunction (49). Besides blood flow, the size of the molecule may affect the passage of the material.

122 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The pore size of the membranes in the blood vessel walls as well as in the epidermis (50) may be smaller than the molecular volume of the sub- stances. For instance, a pore diameter of 55 ,•.. will retain egg albumin (51). Hydrostatic pressure may also affect the passage (52). In other aspects of persorption it has been found recently that the skin color may be controlled by topical application of certain chemicals. The monobenzyl ether of hydroquinone inhibits the oxidation of tyrosine so that melanin formation may be prevented (53). On the other hand, white skin patches of vitiligo may be made darker by using 8-methoxypsoralen along with sunlight. This chemical stimulates tyrosinase activity in the cells of the lower layers of the epidermis (54). This suggests the study of enzymes in the skin which may possibly influence persorption. Acid phosphatase has been found in regions of keratin transition (55). Esterases have been reported in high concentration near the surface (56). Succinic dehydrogen- ase (57) and cytochrome oxidase have also been observed (58). Mon- amine oxidase may be responsible for the ammonia from sweat glands (59). Various aspects of this phase offer a wide field for future research work. Age offers many problems in persorption (60). For instance, estrogenic ointments have been recorded to have a beneficial effect (61) on senile skin though a visible improvement has been questioned in one instance (62). There is some question as to whether the collagenous and elastic tissues change markedly with older age thus affecting persorption (63). Aging of protein, ground substance, hyaluronic acid, hyaluronidase, glycogen and other constituents must be further investigated (64). Observation of cir- culatory changes of both blood and lymph in the dermis along with oxida- tion studies will be of value in considering persorptive measures (65). The scalp (66) should be considered specifically, for it has peculiarities not found in other parts of the skin. Since aging of skin does not necessarily correspond to chronological aging other factors such as skin exposure, nutrition (67), sensitivity and possibly stress (68) should be investigated. Poison ivy (69) and other similar skin reactions are only partly understood with respect to skin penetration and present many research problems. The action of lysergic acid diethylamide (70) on capillary resistance introduces serotonin inhibition for study. Cor- tisone and its derivatives may suppress vascularization through action on the ground substance and hyaluronic acid (71). Temperature, humidity, season and sex also probably contribute to differences in persorption (72). Skin-fold thickness measurements (73) may prove useful to predict persorp- tion values. SUMMARY Due to considerable discussion of terminology for the passage of materials through the skin, a new term '•Persorption" has been proposed. Different