Many snake oil sellers like to include testimonial evidence from users of their product to "prove" how effective it is in promoting hair regrowth. However, there are many problems with this kind of information.

The testimonials included on a web site are selected by the web site owner who is usually the product seller. Obviously, someone wanting to sell a product is not going to post testimonials that tell you the product failed to work. Only the testimonials that show the product in the best light are going to be published.

We all like to believe what others tell us about personal experiences, but separating cause and effect from coincidence can be very difficult. When looking at web sites consider that the people making the testimonials may not actually have had the condition. Even if they did, their recovery may have occurred without the help of the product. Many forms of hair loss, including androgenetic alopecia, are not steadily progressive. They develop in fits and starts. You may even have some partial spontaneous recovery, only to lose it again at a later date.

All of us have more hair loss in autumn and early winter and least hair shedding in spring and early summer. This is because our bodies are subject to the seasons, yes even despite our artificial light and central heated world our bodies still feel the need to change our summer hair "coats" for winter ones.

Other forms of hair loss, such as telogen effluvium, are temporary and do eventually end with just the passage of time. Establishing medical truths requires careful and repeated investigation. With well designed experiments, not reports of coincidences misperceived as cause and effect. That is why testimonial evidence is forbidden in scientific articles, is usually inadmissible in court, and it is not used to evaluate whether or not drugs should be legally marketable. It would be inappropriate and potentially dangerous if government health agencies approved drugs based on testimonial letters or interviews with a few patients.

Finally, some snake oil sellers may simply make up the testimonial evidence for their product.