A sudden indentation in the forehead can be concerning, especially when it appears seemingly overnight and the cause is unclear. There are several possible explanations, and the key is identifying what is happening beneath the skin before trying to correct the indentation. Possible causes include localized loss of subcutaneous fat, changes in the underlying soft tissue, or a condition that causes the skin and deeper tissues to become thinner or tethered. One example is linear morphea, an uncommon inflammatory condition that can cause a groove or indentation on the forehead. Other possibilities include localized lipoatrophy or changes related to previous trauma or inflammation. Although you mentioned having Botox about six months before this appeared, the timing alone does not establish that Botox caused the indentation. Botox temporarily relaxes targeted muscles, but a persistent, newly developed groove is not a typical effect and deserves further evaluation rather than being automatically attributed to the injection. Since two dermatologists have not been able to identify the cause, I would consider seeking an evaluation from a dermatologist experienced in inflammatory skin conditions or a specialist familiar with disorders affecting the deeper soft tissues. Depending on the appearance and examination findings, further investigation may include a skin biopsy or imaging to assess the underlying tissue. I would not recommend jumping straight to filler or another cosmetic procedure until the cause is understood. If the indentation is due to tissue inflammation or progressive tissue loss, treating the underlying condition may be more important than restoring volume. If the area is stable and represents a permanent loss of soft tissue, options such as carefully selected filler or fat grafting may eventually be considered. Because this appeared suddenly, please seek prompt medical assessment if it is deepening or spreading, or if you develop pain, skin discoloration, a severe headache, vision changes, or other new neurological symptoms. The most important next step is establishing whether this is a stable contour change or an active process affecting the skin and underlying tissue. That distinction will guide the safest and most appropriate treatment.