Hello and welcome to healthcaremagic I would think that the peel was stronger this time as compared to last time OR it was kept for a longer time than before, therefore it may have acted more as compared to last time, thus leading on to irritation with resulting post-inflammatory hyperpigmentation. Cosmopeel contains Trichloroacetic acid (TCA) and is considered to be one of the stronger peels. The end point of cosmo peel is frosting and mild erythema, when the peel should be neutralized, immediately. However some times the peel can act more aggressively either because higher concentration is used or it is left for a little longer than the end point, thus causing more frosting and deeper erythema and later post inflammatory hyperpigmentation. I would suggest that you use a moderately potent topical steroid cream, twice daily over the affected area(flutivate cream) for a few days. This would facilitate the superficial dark, dead skin peel off and would also help in resolving post-inflammatory hyperpigmentation. Sun protection with a broad spectrum sunscreen is advisable to prevent sun induced darkening. Regards