Due to its low cost, formaldehyde was commonly used as conservative in hygienic and cosmetic products. However, formaldehyde is strongly reactive and toxic, so its use has been forbidden in several products. Recently, it was reported by different media that formaldehyde has been added illegally in milk, causing innumerous health problems. In this work we developed a colorimetric indicator paper based on Schiff 's reagent, which can be associated with a smartphone application. It was observed that the paper stabilizes the Schiff 's reagent, avoiding its decomposition during short periods. It was also possible to successfully detect the presence of formaldehyde in commercial products, such as: detergents, shampoos and conditioners. Regarding milk based products, the indicator paper is very sensitive to detect formaldehyde, having a sensibility of 0.01% (v/v). The developed indicator paper has low cost and can help the supervision of milk products, as a trial test. Also it is possible to commercialize this product to common consumer, due to its simplicity.
