Infection control: When using ethyl/isopropyl alcohol as a skin antiseptic, which concentration is most effective?

Introduction / Context:
Alcohols are common antiseptics for hand hygiene and skin preparation. Their efficacy depends on concentration: sufficient water content is needed to denature proteins and penetrate cells effectively.

Given Data / Assumptions:

• We are comparing typical concentrations used in clinical practice.
• Effectiveness is judged by rapid bactericidal activity and broad action against vegetative bacteria and many viruses (not spores).

Concept / Approach:
Protein denaturation requires water; very high concentrations (e.g., 95%) dehydrate microbes rapidly, forming a protective protein shell that can reduce penetration and overall kill. Around 70% alcohol provides an optimal balance of water for protein denaturation and lipid membrane disruption.

Step-by-Step Solution:
Consider 95%: too little water → suboptimal denaturation despite strong dehydration. Consider 50% or lower: insufficient alcohol content for reliable rapid kill. Identify 70% as the standard, widely recommended concentration for antisepsis.

Verification / Alternative check:
Guidelines and infection control manuals consistently cite approximately 70% ethanol/isopropanol as optimal for skin antisepsis, balancing efficacy and evaporation rate.

Why Other Options Are Wrong:
95% lacks adequate water for optimal denaturation; 25–50% is too dilute for consistent, rapid action.

Common Pitfalls:
Assuming “stronger is always better.” For alcohol antiseptics, a mix with water maximizes protein denaturation and biocidal activity.

Final Answer:
70%.