What Is a Coma?

A coma is when someone is unconscious for an extended period of time. Their eyes are closed and they do not respond to sounds or other things in their environment. They can't be awakened, even with vigorous or painful stimulation.

A coma is not the same as sleep. In a coma, the brain doesn't go through normal sleep cycles. Someone who is sleeping may move if they're uncomfortable, but a person in a coma will not.

In this article, you'll learn what causes comas, what it takes to recover from a coma, and what some similar states of unconsciousness are.

Patient in intensive care unit
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What Causes a Coma?

Many types of illnesses and injuries can damage your brain cells and put you in a coma, including:

Most comas only last a few weeks, though they can last longer—even years. This largely depends on what caused the coma in the first place.

And if enough nerve cells die in a region of the brain that's essential for maintaining wakefulness, the person will probably never regain normal consciousness. These regions include:

  • Thalamus: Sitting low in the back of your head, this region plays a role in movement, processing information from your senses, sleep, and alertness.
  • Brainstem: Just beneath the thalamus, the brainstem connects your brain and spinal cord. It has roles in breathing, heart rate, balance, coordination, and reflexes.
  • Large portions of the cerebral cortex: Outer layer of gray matter on the brain. It forms connections between areas of the brain and is involved in a vast array of functions.

Nerve cells can regenerate, but they do so only in specific parts of the brain. Plus, it's a very slow process if it does occur.

Technically speaking, though, there are other causes of someone being in a comatose state.

Doctors put people into coma every time they use general anesthesia. However, most people wake up after a few hours once their bodies process the medication.

The definition also includes people who are unconscious due to medications, toxins, or infections. As with anesthesia, they generally wake up when the body rids itself of whatever caused the unconsciousness.

What Happens During a Coma

During a coma, brain activity is minimal. Most of the body continues to function as it works to heal itself and come out of that state. However, there's no awareness.

A comatose person may move in ways that seem like they're awake, which can be misleading to friends and family. For example, they may grimace if something causes pain.

They may even appear to move away from pain. In what's called Lazarus syndrome, an especially strong reflex can lead someone in a coma to sit upright.

However, these responses are just reflexes. It's similar to what happens to your leg when a healthcare provider taps your knee with a hammer. These movements don't mean someone is awake, aware, or improving. These are simply automatic movements.

Recovering From a Coma

Whether someone can recover from a coma depends on many factors, including what put them there in the first place.

For example, a coma from traumatic brain injury tends to have a better prognosis than a coma from cardiac arrest.

Younger patients tend to do better than older ones. Someone in a drug-induced coma may wake naturally as the drug is cleared from their system.

But someone with a permanent brain lesion may progress to a lasting vegetative state, in which they appear awake but are unresponsive. It can also lead to brain death.

In general, the longer someone remains unconscious, the less likely they are to recover their alertness. However, the only way to know for sure whether someone will recover from a coma is to wait for a reasonable amount of time and see.

How much time to wait can be a hard decision. It depends on the unique circumstances of the person and their loved ones. A patient's medical team can provide helpful information to guide next steps.


A coma is a condition involving unconsciousness, closed eyes, and an inability to be awakened. Some causes include head injury, seizure, brain damage or infection, stroke, drug overdose, or very low blood sugar. If damage is severe enough in certain brain regions, the person is unlikely to ever come out of the coma.

Other States of Unconsciousness

The same injuries and illnesses that put people in a coma can also lead to other states of unconsciousness. The four different states, from least to most severe, are:

  • Minimal consciousness
  • Coma
  • Vegetative state
  • Brain death

Someone in the first three states may transition between them. For example, they may go from a coma to minimal consciousness. That may indicate healing, but it doesn't always mean they'll wake up.

Someone may go from a coma or vegetative state to brain death if their body can't repair the damage.

Minimal Consciousness

Minimal consciousness is a less serious state than a coma. Doctors often hope for signs that someone is minimally conscious rather than in a true coma or vegetative state.

Minimally conscious people are largely unaware of what's going on around them. They have enough brain activity, though, to have some glimmer of preserved awareness of themselves or the surrounding environment.

This may mean:

  • A consistent ability to follow simple commands
  • Appropriately giving yes/no responses
  • Demonstrating purposeful behavior (appropriate smiling or crying, adjusting their hands to the size and shape of held objects)

Someone may transition to a state of minimal consciousness or recover from it. It's also possible for someone to remain minimally conscious indefinitely.

In general, people in a minimally conscious state have much better outcomes than those in sustained comas. Even so, many people who recover from this state remain seriously disabled.

Vegetative State

Whereas comatose patients appear to be sleeping, people in a vegetative state regain some degree of crude arousal, resulting in the eyes being open.

The eyes may even reflexively move, appearing to gaze at things in the room. However, these people don't show any true awareness of themselves or their environment. Brain activity in the areas that control consciousness is reduced.

If the brainstem is intact, the heart, lungs, and gastrointestinal tract continue to function. If not, machines may be needed to keep these functions going.

If this condition lasts for months, it's considered a persistent vegetative state (PVS).

This can be permanent. If medical care continues, it's possible for someone to remain alive in a persistent vegetative state for decades.

Brain Death

Brain death means the person is dead. It occurs when brain function stops in the whole brain, including the brainstem. At this point, the person can no longer breathe on their own. If machine support is removed, they'll typically go into cardiac arrest.

There are no well-documented cases of meaningful recovery in people accurately diagnosed with brain death. It's considered impossible to revive them.

While a qualified physician can make a diagnosis of brain death based on the physical exam alone, given the seriousness of the diagnosis, some families prefer to have additional tests done as well.

However, if the bedside exam can be done completely and accurately, additional tests are unlikely to show any new or more hopeful information. Because the brain has been deprived of blood and oxygen, autopsies generally show that much of the brain has wasted away.


Minimally conscious people may be able to respond to questions and follow simple directions.

Someone in a vegetative state may appear more aware than someone in a coma, but they're not. Brain death occurs when someone who's comatose will die without machine support.


A coma is a state of unconsciousness you can't be awakened from. The brain doesn't go through normal sleep cycles and you can't move in response to pain. Comas are caused by brain damage from head injuries or illness.

If damage is in certain key regions of the brain, recovery may not be possible. Age and the cause of the coma are other factors affecting recovery. The longer it lasts, the less likely recovery is.

Other states of unconsciousness exist, as well. Minimally conscious people retain some awareness and ability to respond. At the other end of the scale is brain death, which means the brain no longer has any activity and the person is dead.

A Word From Verywell

If someone you care about is in a state of unconsciousness, ask their medical team what state they're in and what kind of awareness they may have.

Understanding the different possible states may influence your actions around the unconscious person and help guide your decisions regarding their care.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Institute of Neurological Disorders and Stroke. Coma information page.

  2. American Academy of Neurology. What is the difference between coma, minimally conscious state, persistent vegetative state, and brain death?

  3. Nemours KidsHealth. What Is a Coma?

  4. Geocadin RG, Callaway CW, Fink EL, et al. Standards for studies of neurological prognostication in comatose survivors of cardiac arrest: a scientific statement from the American Heart Association. Circulation. 2019;140(9):e517–e542. doi:10.1161/CIR.0000000000000702

  5. Harvard Health Publishing. The book of neurogenesis.

  6. Sahni V. The Lazarus phenomenonJRSM Open. 2016;7(8):2054270416653523. doi:10.1177/2054270416653523

  7. Dana Foundation. Disorders of consciousness: brain death, coma, and the vegetative and minimally conscious states: report on progress.

  8. Fins JJ. Neuroethics and disorders of consciousness: discerning brain states in clinical practice and research. AMA J Ethics. 2016;18(12):1182-1191. doi:10.1001/journalofethics.2016.18.12.ecas2-1612

  9. Johns Hopkins Medicine. The challenges of defining and diagnosing brain death.

By Peter Pressman, MD
Peter Pressman, MD, is a board-certified neurologist developing new ways to diagnose and care for people with neurocognitive disorders.