Induction Phase
Approximately 0.2 mL or grams of each test article is applied to the subject's back, using occlusive patches. Semi-occlusive tape may be recommended when evaluating known irritating and/or volatile materials.

Twenty-four hour patch applications are generally made on a Monday, Wednesday, Friday schedule. Twenty-four hour rest periods follow Tuesday and Thursday removals and a 48-hour rest period follows the Saturday removal. The site is scored by a trained ETC examiner just prior to the next patch application. This procedure is repeated until 9 inductions of the test article are made on the same skin site.

If a subject develops a level 2 reaction or greater during the Induction phase, the patch is applied to an adjacent fresh site for the next application. If a 2 or greater reaction occurs on the new site, no further induction applications are made. However, any reactive subjects are subsequently patched with the test article on a virgin test site during the Challenge phase of the study.

Challenge Phase
Approximately 2 weeks after application of the last induction patch, a challenge patch is applied to a previously unpatched (virgin) site, adjacent to the original induction patch site. The challenge site is scored 24 and 72 hours after application. The subjects are asked to report any delayed reactions which might occur after the final challenge patch reading.

Skin responses are scored according to the following 6-point scale:
0 = (None) No evidence of any effect.
+ = (Barely perceptible) Minimal, faint, uniform or spotty erythema.
1 = (Mild) Pink, uniform erythema covering most of the contact site.
2 = (Moderate) Pink-red erythema, uniform in the entire contact site.
3 = (Marked) Bright red erythema with/without petechiae or papules.
4 = (Severe) Deep red erythema with/without vesiculation or weeping.

Accompanying edema (swelling) at any test site is recorded with an "e" and described as mild, moderate or severe. Other possible dermal sequelae are similarly recorded.