Most skin bacteria can grow under all pH conditions normally found on skin, but many bacteria possess individual pH optima for growth; therefore, small changes in pH have the potential to provide an ecological advantage to those finding more favorable conditions with regard to hydrogen ion concentration. Studies have shown that increased skin hydration resulting from occlusion is accompanied by an increase in pH, from its normal slightly acidic condition to near neutrality (5). pH can also exert an effect on microbial populations by altering the antimicrobial properties of fatty acids on the skin. The protonated form of the acid is more active than the unprotonated form, so as the pH approaches the pKa of the acid, antimicrobial activity increases. As microorganisms vary in their susceptibility to fatty acids, relatively small changes in pH can influence the numbers and kinds of organisms that thrive in a population.
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