PRIMARY IRRITATION OF THE SKIN 219 Assessment of irritation Assessment is carried out immediately before applications are made during the first 4 days of the test. On the fifth day, assessment is carried out 24 h after the last (fourth) application of test material. The following numeri- cal scale is used for recording irritation: 0 = No visible blood vessels or erythema. 2 = Few blood vessels, barely visible. No erythema. 4 = Main blood vessels visible on lower half of ear. Slight erythema over lower third or base of ear. 6* = Main blood vessels more obvious. Suggestion of capillary network at tips of main vessels. Slight or generalized erythema. 8, = Main blood vessels extend to edge of ear. More extensive capillary network between main blood vessels. Possibly internal haemorrhage erythema more pronounced. Ear may begin to fold back and lose suppleness. 10 -- Pronounced blood vessels and extensive capillary network evident. Marked erythema. Possibly 'frilling' of ear margin. 12 = Pronounced blood vessels and extensive capillary network ex- tending to ear margins. Severe erythema. 'Frilling' and thickening of ear margins. Crusting more in evidence. 14 = Pronounced blood vessels and severe erythema. Obvious thicken- ing of ear. Possibly necroses. Crusting may extend over whole ear surface. Interpretation The daily differences between control and treated ears for each animal are summed to give an overall total for all the mice in an experiment. A correction is made for any difference between control and treated ears initially. The total, divided by 5, yields a mean for each test material for the experimental period. The data obtained in this way may, in our experience, be interpreted thus: 0-9: Probably not perceptibly irritant to human skin. 10-15: May be slightly irritant to some users. Over 15: Likely to prove sufficiently irritant to some users so that level of complaints might be unacceptable. Human patch test Finkelstein, Laden and Miechowski (2) published details of a method of *From this stage onwards, fine dry scaling may be seen with increasing severity. •'From this stage onwards, crusting may occur with increasing severity.

220 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS conducting a human patch test to assess primary irritancy (not to establish sensitizing potential), with intermittent application of patches and pre- cautions to avoid excessive skin damage. Their technique thus embodies the main requirements for a test to be applied frequently in a cosmetic re- search laboratory without constant, direct medical supervision. The modi- fications shown below are the result of our own experiences of using this type of patch testing procedure. Cosmetics are mostly applied to the skin without occlusion but in order to expedite irritant skin response for experi- mental purposes, it is usually preferable to carry out tests under conditions of occlusion, i.e. using 'dosed' rather than 'open' patches. However, many cosmetic formulations include readily volatilized solvents such as ethanol which only remain on the skin for a brief period and do not cause irritation, though they would certainly prove irritant under occlusion. Formulations of this nature should be applied to the patch material 15 min before placing on the skin, to exclude irritation due to the volatile solvent. Derrnicel surgical tape* 7.5 cm wide serves as the support for 125 mm squares of lint. Before being cut, the lint is backed with Blenderrn surgical tape• to ensure occlusion (since Dermicel is not occlusive). The Blenderrn- backed lint squares are positioned 250 mm apart and readily adhere to the Dermicel tape (Fig. I). Patches may be prepared for use in pairs, fours or sixes, stored in a roll and only cut for use when needed. The preparation of sufficient patches for a test on 50 subjects takes about 8 man h. Panels of volunteers A panel of 40-50 subjects, comprising equal numbers of male and female volunteers, is suitable. Individuals with known allergic reactions, hay-fever and asthma are excluded. Site of application For simplicity and speed and also to facilitate the use of panels including male and female subjects, patches are applied to the upper arm, towards the inner aspect. The Dermicel readily stays in position on the arm without any retaining bandage (Fig. 3). The positions of the materials to be tested are randomized on each subject in order to minimize effects due to variation within the area of skin *Supplied by Johnson & Johnson Ltd, Slough, England. tSupplied by The 3 M Company, London.