In the simplest terms, acute conditions are short-term while chronic conditions are long-term. However, these two ways of categorizing an illness, disease, pain, or other condition involve many other differences aside from duration of the condition.
Deeper dive
Acute illnesses are those that tend to have a definitive start and end (the patient or their physician can identify when the condition started and when it has stopped). They also generally affect one or a few specific, identifiable body parts, organs or systems. Most of the time, acute illnesses respond to medication or other treatments, or they resolve on their own over time (e.g., a broken bone healing, a common cold infection eventually defeated by the immune system, etc.). The causes of acute infections or conditions are also usually pretty straightforward.
Chronic illnesses, in addition to affecting a person over a longer period of time, tend to be more complex in general and may not have easily identifiable or isolated causes, or they may have multiple causes. Chronic conditions often involve multiple body areas, organs or systems, or even the entire body. They may or may not respond to treatment, or treatment options for them may not exist. Chronic conditions may require multiple treatment strategies or shifts in treatment. Cancer, for example, is a chronic condition that can affect up to the entire body and may require radiation, surgery and/or multiple drugs, and physicians may need to switch strategies over the course of the illness. An Ebola virus infection, however, is acute even though it may affect the entire body. Treatment of chronic conditions, then, is typically more complex than that of acute conditions and may focus on management, quality of life, self-care and coping skills. With acute conditions, the goal is a cure or healing.
Broadly speaking, chronic illnesses tend to have a greater impact on quality of life, but an acute illness can certainly have intense short-term effects on quality of life and can result in a chronic condition. For example, measles is an acute disease (with a seriously unpleasant short-term experience), but if complications from the measles cause deafness, then the hearing loss becomes a chronic condition requiring management, even if that management is occupational therapy to learn new ways of living. Or, an acute condition may cause a temporary chronic one, such as frequent coughing over several months caused by a pertussis infection, even if the active pertussis infection resolves within the first month. Or, an acute injury, such as a leg laceration, can lead to a permanent disability if the leg requires amputation or if an individual loses function in the limb.