Yogurt

Topical yogurt (typically used as a DIY soothing/humectant ingredient) is a complex, non-standardized mixture containing lactic acid, proteins, fats, live cultures, and residual milk components; variability in acidity and composition makes irritation outcomes unpredictable, especially on eczematous or barrier-compromised skin. Clinical patch testing data for fermented dairy used directly on skin is limited, but the combination of low pH (from lactic acid) and potential contact reactivity to milk proteins/fragrance/flavor additives in consumer yogurts justifies a moderate irritancy score and routine patch testing for sensitive patients. Safety Notes: In commercial skincare, yogurt (typically fermented milk/"yogurt powder", yogurt extract, or yogurt filtrate) is used at very low levels (~0.05–1%) when included mainly for marketing/skin-conditioning in leave-on creams/serums and in rinse-off cleansers. Higher-use products marketed as “yogurt masks,” “probiotic/fermented dairy” packs, and some soap/cleansing bars can incorporate substantial yogurt or yogurt solids, commonly ~5–30% and in a few consumer-available artisan or specialty rinse-off/mask formats reaching ~50–80% (with water activity/microbial control and odor/stability constraints being the primary practical limits).