The indication CPs must always be based on etiopathogenic criteria and anatomopathological correlations.

The depth of absorption of a substance through the skin is a consequence of the “dynamically interactive variables” which include skin thickness, density of appendages, and degree of oiliness, integrity of the skin barrier, drug concentration, and volume of agents, rubbing and occlusion. All these details must be simultaneously considered at the time of the application.

TCA stands out for its safety and versatility. It can be used alone for very superficial and superficial peels, combined with other substances for medium depth peels, and with other procedures at the same moment, without systemic toxicity, even in large extra-facial areas.

TCA can be used on the skin only up to 45%. It has a very intense caustic power and is more potent than phenol at maximum concentration. Its action is slow and the erythema and frosting should always be expected within some minutes before the application of a new layer.

The use of 5% 5-FU, twice daily during the 7 days preceding medium 35%–45% TCA CPs, may be a therapeutic alternative for the treatment of multiple actinic keratosis, including the cancerization field.