Your loved one with dementia may need help with self-care and other routine activities for many reasons. They may not understand why some things need to be done, they may not understand how to perform these activities, or they may have poor coordination and movement issues.
Dementia is a progressive disorder, which means that the person needs more assistance as their health declines. For example, in the first stages of dementia, your loved one may only need to be reminded to have diner. Later, the person may need to be reminded of specific steps in feeding (to open their mouth, chew, swallow, etc.). After some time, the person may not be able to feed themselves, or they may lose interest in eating, so the amount of help they need increases.