Propylene glycol dermatitis: re-evaluation of an old problem

Area of Science:

• Dermatology
• Toxicology
• Allergology

Background:

• Propylene glycol (PG) is a common ingredient in consumer products, but evaluating associated dermatitis is difficult.
• Existing research on PG-induced skin reactions lacks a unified classification system.

Purpose of the Study:

• To revisit existing research on skin reactions to propylene glycol.
• To propose a new classification system for propylene glycol-induced dermatitis.
• To outline future research directions for a comprehensive understanding of PG skin reactions.

Main Methods:

• Literature review of studies on propylene glycol (PG) and skin reactions.
• Analysis of author's own observations.
• Proposal of a four-mechanism classification for PG-induced skin reactions.

Main Results:

• A proposed classification of PG skin reactions into four mechanisms: irritant contact dermatitis, allergic contact dermatitis, non-immunologic contact urticaria, and subjective or sensory irritation.
• This classification offers a partial explanation for observed PG effects.
• Challenges remain in distinguishing between irritant and allergic reactions and determining PG's irritation threshold and optimal patch test concentrations.

Conclusions:

• The proposed four-mechanism classification provides a framework for understanding propylene glycol (PG) dermatitis.
• Further research, including repeated patch tests, open application tests, oral challenges, and biopsies, is necessary for a complete evaluation.
• Clarifying objective criteria for differentiating reaction types and establishing standardized testing protocols is crucial.