The word "unnoticed" means not being noticed or observed. It describes something that has happened or been done without anyone realizing it, often because they were not paying attention or did not see it happen.
Hearing loss often goes unnoticed in dogs until it becomes severe. (lovinmypup.com)
Why do so many absolutely fantastic indie titles go largely unnoticed by the gaming community? (elder-geek.com)
Because many food allergies are relatively mild and the allergens are often found in foods we eat every day, food allergies often go unnoticed for years and years. (besynchro.com)