130 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS shows up earlier and is more severe at the high concentration of 1 per cent than at the lower levels. No irritation was observed at a level of 0.1 per cent NaLS alone. The skin shows marked erythema, thickening and deep lesions with bleeding after ten daily applications of the one per cent NaLS. In the course of the ten to fourteen day interim period the gross irritation disappears. Three daily challenge applications (2nd stage) did not induce any gross skin irritation. Histologically there is a thickening of the epi- dermis and evidence of cellular infiltration. Ten daily applications of the mixtures of NaLS and NiSO4 resulted in irritation at each concentration of NaLS which appeared sooner and in most instances more intense then for NaLS alone at the corresponding levels. In the second stage after three challenge applications severe irritation resulted with the NiSO4 in combination with 0.5 and 1.0 per cent NaLS. Histologically, the skins were acanthotic, showed cellular infiltration and Ni was present in the pilosebaceous apparatus, dermis and the basal layer of the epidermis. The reaction to NiSO4 was evident in the presence of 0.1 per cent NaLS but to a lesser degree than at the higher levels of NaLS. Skin pretreated repeatedly with NaLS alone becomes vulnerable to deep penetration of Ni when the latter is applied alone in the challenge stage. Untreated skin is not penetrated by NiSO4 when applied alone. This finding recalls the recent work of Skog (5) and Baer and co-workers (6) who pointed up the importance of acanthosis in triggering skin response to known sensitizers. TABLE 2--INFLUENCE OF SODIUM DODECYL BENZENE SULFONATE ON THE ECZEMATOGENIC ACTION O1• NISO4 REPEATEDLY APPLIED TO OUINEA PIG SKIN Skin Gross Skin Appearance Reading* After Daily Applications After Two Re- Skin peat Reading* Challenge Histological Group Test System Onset of After 10 Ap. plica- Analysis No. DDBS NiSO4 Irritation Applic. nons After Challenge 1 1.0% 2 1.0% 0.5% 0.5% 0.5% 6 0.2% 7 0.2% 10 applic. 1 0 Acanthotic 01•o 8 applic. 3 3 Acanthotic Ni in hairduct, dermis and Malpighian layer 10 applic. 1 0 Acanthotic 01•% 8 applic. 3 3 Same as (2) 0.1% 10 applic. 1 0 S1. Acanthotic sl. penetration of Ni into hairduct not in dermis No irrit. 0 0 S1. Acanthotic 01•% No irrit. 0 0 Same as (5) 0.5% No irrit. 0 0 Normal Ni does not penetrate skin 5.0% No irrit. 0 0 Same as (8) * Skin Readings: O--No irritation 1--Erythemia, roughness 2--Erythema, slight thick- ening, crusting and trauma 3--More advanced stage of (2) 4--Deep lesions and bleeding.

PERCUTANEOUS ABSORPTION AND SURFACE ACTIVE AGENTS 131 Irritation and histological findings with the NiSO4 and sodium dodecyl- benzenesulfonate systems are given in Table 2. The effects are similar as found for the NiSO4-NaLS mixtures. However, DDBS alone or in com- bination with NiSO4 did not cause the severe cutaneous responses as found with the NiSO4-NaLS systems. In fact at the 0.2 per cent level, DDBS alone or in combination with NiSO4 resulted in no irritation or penetration of NiSO4. A summary of the findings with NaLS and DDBS along with the results obtained with other surface active agents is given in Table 3. Photographs of guinea pig skin treated with NiSO4 alone, NaLS alone, NiSO4-NaLS and NiSO4 with Igepon A are shown in Fig. 1. TABLE 3--RELATIVE EFFECTS OF SUKFACE ACTIVE AGENTS IN ELICITING THE ECZEMATOGENIC EFFECT OF 0.5% NISO4 ON GUINEA PIGS (Two STAGE MULTIPLE APPLIC. TEST) Agent Concn. ß -Skin Response , ----lst Stage---- . . 2nd Stage-----, Deep Pene tr a- tion* of Irritation Thicke•ning Irritation Ni NaLS 0.1 Slight Slight Moderate 0.2 Moderate Moderate Moderate q- 0.5 Marked Marked Marked q- 1.0 Marked Marked Marked q- DDBS 0.2 None Slight None - 0.5 Moderate Moderate Moderate q- 1.0 Moderate Moderate Moderate q- Igepon A 1.0 None None None -- Igepon T 1.0 None None None - Soap 8.0 Slight Moderate None - Sterox A J100 1.0 Slight None None - Brij 35 1.0 None None None - Arquad 2HT 1.0 None None None - * (q-) signifies Ni penetration of pilosebaceous apparatus, dermis and basal layer of epider- mis. (-) signifies no penetration. Soap at a level of 8 per cent alone or with NiSO4 causes no cutaneous reaction other than moderate thickening in both stages of the multiple application test. The absence of a cutaneous reaction by nickel in the presence of soap is probably due principally to the fact that the nickel soap which forms by metathesis is very insoluble and does not penetrate into the dermis. Other artionic agents tested, Igepon A and Igepon T at a 1 per cent level, alone or with 0.5 per cent NiSO4 were without any cutaneous effect in both stages. The two nonionics Brij 35 and Sterox AJ-100 and the cationic, Arquad 2HT, at the 1 per cent levels, were without effect on skin alone or in inducing the allergenic response of Ni. Histologically, treatment with these mixtures did not result in the percutaneous absorption of nickel.