Sun and Botox - Where the chemical was injected created a pigment mark. Why did this happen and what can I do?

The pigmentation is unrelated to Botox. Melasma is a common pigmentation problem that often affects the forehead. Unfortunately, it is a difficult problem to cure. Getting it under control requires strict sun protection, Retin A, hydroquinone, and chemical peels. I also recommend Heliocare, which is a fern extract that is an antioxidant and helps with protecting the skin from the sun.  See link

Thank you for your question LJ11111. I
am sorry to hear about your situation. Botox is a purified protein used to
address wrinkles associated with facial expression. Melasma is a condition characterized by the appearance of dark patches on the skin. Melasma can be triggered by sun exposure or other insults such as injections. It is difficult to assess your skin without photographs. Melasma can be treated with a variety of products and treatments, as can other pigmented conditions. Please consult with a doctor for specific
recommendations.  Good luck!