From Wikipedia: "Polydimethylsiloxane (PDMS) belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or flow) properties. PDMS is optically clear, and, in general, inert, non-toxic, and non-flammable. It is also called dimethicone and is one of several types of silicone oil (polymerized siloxane). Its applications range from contact lenses and medical devices to elastomers; it is also present in shampoos (as dimethicone makes hair shiny and slippery), food (antifoaming agent), caulking, lubricants and heat-resistant tiles."
It is chemically inert. That is, it doesn’t have a tendency to chemically react with other molecules in the body. In Dr. Fukuda’s work, it’s not even directly applied to the body (of the subject mice in the test.) Instead, it’s put in a laboratory culturing vessel along with stem cells and epithelial cells, and helps them grow into a mini hair follicle (called a Hair Follicle Germ).
The articles that say “an ingredient in McDonald’s fries may cure baldness” are misleading – that’s just click bait. If this chemical is applied directly to your skin, it won’t grow any hair.