INTRODUCTION
Keratosis pilaris (KP) is a skin condition that presents as hyperkeratotic, and at times erythematous, follicular papules typically found on proximal extremities of patients with a background of atopy. While a common skin finding, the available treatments are limited to minimally effective topical emollients, exfoliants, and retinoids. As such, newer, more efficacious options are needed to relieve the visual and textural abnormalities caused by this condition.In the last century, the improvement in hygiene practices and overall cleanliness of modern society has dramatically reduced exposure to diverse environmental microbiota that have traditionally assisted in immune and proliferative regulation. As a result, certain conditions such as atopic dermatitis, seasonal allergies, and asthma have increased in prevalence.1,2 Furthermore, improved societal hygiene has resulted in the near elimination of cutaneous commensal ammonia oxidizing bacteria (AOB). AOB produce nitric oxide (NO) and nitrite products through the oxidation of ammonia in sweat.1,3 NO is a ubiquitous gas that functions as a signaling and effector molecule that regulates keratinocyte proliferation, and healthy physiologic levels of NO in the skin result in decreased keratinocyte proliferation.4,5 Therefore, as the presence of AOB has essentially become nonexistent in developed societies, so has the availability of an important source of proliferation-stabilizing NO in humans. We propose that restoring this dermal microflora with a purified strain of AOB, Nitrosomonas eutropha (D23), may replenish physiologic NO levels and restore its anti-proliferative role on keratinocytes. Furthermore, as KP is primarily a disorder of hyperproliferative keratinization leading to follicular plugging, we hypothesize that D23 would be an effective treatment for this condition.
METHODS
A 4-week single-center, double-blind, placebo-controlled, split-arm study was performed to evaluate the safety and efficacy of an ammonia-oxidizing bacteria (AO+) spray-on mist for the treatment of keratosis pilaris. Enrolled subjects were aged 18-65 years with Fitzpatrick skin types I-IV and had a clinical diagnosis of keratosis pilaris involving proximal extremities. Exclusion criteria included concurrent pregnancy, prior laser therapy to the extremity in the past year, a separate on-going
