pH 4 Underarm Lotion: What the 2015 Trial Found

A pH 4 lotion reduced underarm odor compared with untreated skin in a small 2015 trial. Its advantage over a pH 5.8 lotion was not statistically significant. Those are different comparisons.¹

What the women used

The randomized, single-blind crossover study analyzed 44 women aged at least 60. Each emulsion was applied once daily for three days, with the other underarm untreated. Six odor judges assessed smell eight and 24 hours after the final application.¹

At both times, pH 4 performed better than untreated skin. The direct comparisons with pH 5.8 produced p-values of 0.078 and 0.053, respectively, above the study’s 0.05 threshold. The findings do not establish equivalence between the lotions either.¹

Researchers tested a water-in-oil emulsion, not toner. Sponsor August Wolff employed three authors. The short treatment periods do not establish long-term effectiveness or safety, or results on underarms with active skin disease, which was excluded.¹

Why the pH number is only part of a product

FDA² explains that the exfoliating effect of an alpha hydroxy acid depends on the acid type, its concentration, the product’s pH and the other ingredients. A matching pH does not make two formulas interchangeable. Glycolic acid and lactic acid are common AHAs.²

Before treating a toner as an underarm deodorant, check its intended use and warnings. A facial exfoliant’s percentage and a lotion’s pH answer different questions. The trial above does not supply application directions for the bottle on your shelf.

FDA² has received reports of burning, rash, swelling, pigment changes and other adverse effects from AHA products. Its general advice is to follow directions and warnings carefully. That safety information concerns AHAs as a category; it does not mean those reactions occurred in this lotion trial.²

AHAs can also increase sun sensitivity. FDA² advises sunscreen, protective clothing and limiting sun exposure during use and for a week afterward. This matters when treated skin is exposed in sleeveless clothing. A lower-pH claim is not a reason to ignore that warning.²

Decide whether the target is odor or wetness

The American Academy of Dermatology³ distinguishes the jobs: antiperspirants reduce sweating; deodorants mask or stop odor. If your main difficulty is soaked shirts, choose the treatment discussion around wetness rather than assuming an odor result answers it.³

The academy also suggests recording when heavy sweating occurs and what you were doing. Heat, caffeine, spicy foods and emotional stress can be triggers, but they vary between people. Bring that pattern into a dermatology appointment if sweating interferes with daily life.³

Our deodorant and antiperspirant comparison explains the product categories.

Arms Up uses a Fresh Log to separate body area, wetness, odor and interference with daily life. For an underarm product, record odor and shirt wetness separately, alongside any skin symptoms and the product used. That gives you something specific to discuss before adding another acid or a stronger product.