Heavy metal use in cosmetics poses detrimental health risks. In the United States, 41% of consumers aged 30 to 59 use makeup daily, and over 90% of cosmetics contain one or more of the following toxic elements: mercury, lead, or cadmium. Heavy metals are often used in cosmetics to boost their function. For example, mercury in whitening creams inhibits melanin production, a substance responsible for skin pigmentation. When cosmetics are directly applied to the skin, metal ions enter the body through hair follicles and sweat pores then reach the bloodstream, allowing it to bind to proteins, disrupt their function by accumulating in various organs, causing health issues such as dizziness, insomnia, neurological damage. Therefore,monitoring heavy metals in cosmetic products is essential. However, current testing requires specialized laboratories, trained personnel, and complex procedures. Our project aims to develop an in vitro test solution that detects heavy metals in cosmetics. The presence of metal ions will bind to metal-responsive proteins, triggering the corresponding promoter to initiate the translation of fluorescent protein genes, revealing different colors. It will not only empower consumers to test their products at home but also enable cosmetic manufacturers to evaluate the composition of raw materials.