You can tell someone has a concussion by watching for a combination of physical, cognitive, and behavioral changes after a blow or jolt to the head. Not every concussion looks the same, and some symptoms show up immediately while others take hours or even days to appear. Knowing what to look for, and what counts as an emergency, can make a real difference in how quickly someone gets the right care.
Physical Signs You Can See Right Away
The most obvious signs tend to be physical. Right after a head impact, look for a dazed or stunned expression, loss of balance, slow or clumsy movements, and vomiting. The person may briefly lose consciousness, though most concussions happen without a blackout. They might hold their head, squint against light, or seem unsteady on their feet.
One reliable thing to check is the person’s pupils. If one pupil is noticeably larger than the other, or if the person reports double vision, that’s a serious warning sign. Slurred speech, weakness on one side of the body, or numbness also point to something more severe than a mild concussion and need immediate medical attention.
Thinking and Memory Problems
Concussions disrupt how the brain processes information, and this often shows up as confusion or mental slowness. The person may struggle to answer simple questions: what day it is, where they are, or what happened just before the injury. They might repeat the same question multiple times without realizing it, or seem unable to concentrate on what you’re saying.
Other cognitive signs include feeling “foggy” or “groggy,” difficulty thinking clearly, trouble with short-term memory, and a noticeable slowdown in how quickly they respond. These symptoms can be subtle. Someone might seem mostly fine but take unusually long to answer questions, lose their train of thought, or forget instructions they were just given. If you know the person well, you’ll often notice something feels “off” before you can pinpoint exactly what it is.
Mood and Emotional Changes
Concussions frequently cause emotional shifts that are easy to overlook. The person may become unusually irritable, anxious, or tearful for no clear reason. They might snap at people, seem restless, or appear more emotional than the situation warrants. Sadness and nervousness are also common, even in someone who doesn’t typically experience those feelings. These emotional symptoms can appear within hours of the injury or develop gradually over the following days.
Symptoms That Show Up Later
Not all concussion symptoms are immediate. Some people feel fine for hours after a head injury, only to develop headaches, difficulty sleeping, sensitivity to light or noise, or increasing confusion later that day or the next. This delayed onset is one reason it’s important to keep a close eye on someone for at least 24 to 48 hours after a head impact. Symptoms that worsen over time, rather than gradually improving, are a particular concern.
Sleep disruption is a common delayed sign. The person may have trouble falling asleep, sleep much more than usual, or feel exhausted despite sleeping a normal amount. Persistent headaches that don’t respond to rest are another hallmark.
How Concussions Are Assessed
There’s no single test that definitively diagnoses a concussion. Instead, healthcare providers use structured evaluations that combine several types of checks. The most widely used tool in sports settings is the Sport Concussion Assessment Tool (now in its sixth version, SCAT6), which tests orientation, memory, concentration, balance, and coordination in a specific sequence.
A typical assessment starts with observable signs and basic neurological checks, then moves to questions that test memory and awareness (“What venue are we at? Which half is it? Who scored last?”). Balance is tested by having the person stand in increasingly difficult positions, walk heel-to-toe on a line, or walk while performing a mental task at the same time. After about 15 minutes, the person is asked to recall a list of words they were given earlier to check delayed memory.
Eye movements are another important piece. A screening called the Vestibular/Ocular-Motor Screening tests how well the eyes track moving objects, shift quickly between targets, focus on something close, and maintain stable vision while the head moves. Problems with any of these can signal that the brain’s ability to coordinate vision and balance has been disrupted, even if the person otherwise seems okay.
Blood Tests and Brain Scans
A standard CT scan or MRI won’t show a concussion. These imaging tools are designed to detect structural damage like bleeding or skull fractures, not the microscopic cellular disruption that causes concussion symptoms. Doctors order a CT scan when they suspect something worse than a concussion: persistent loss of consciousness, worsening confusion, seizures, or signs of a skull fracture like bruising behind the ears.
A newer option is a blood test that measures two proteins released by damaged brain cells. The FDA-cleared test (Abbott’s i-STAT TBI cartridge) works with a simple blood draw and returns results in about 15 minutes at the bedside. It’s approved for adults within 24 hours of injury and helps doctors determine whether a CT scan is needed. A negative result makes it less likely that there’s bleeding in the brain, potentially sparing the patient from unnecessary radiation. The test doesn’t diagnose a concussion on its own, but it adds a useful data point alongside the clinical evaluation.
Spotting a Concussion in Young Children
Babies and toddlers can’t tell you they have a headache or feel foggy, so you have to rely entirely on behavioral changes. In addition to the physical signs that apply to all ages, watch for inconsolable crying, refusal to nurse or eat, changes in sleep patterns, and loss of interest in favorite toys or activities. A toddler who suddenly becomes unusually clingy, fussy, or listless after a head bump warrants medical evaluation. In infants under 12 months, any head injury with visible symptoms should be treated as an emergency.
Danger Signs That Need Emergency Care
Most concussions resolve on their own with rest, but certain symptoms after a head injury signal a potential emergency. Call 911 or go to the emergency department if you see any of the following:
- Seizures or convulsions (shaking or twitching)
- Repeated vomiting (not just once)
- Inability to recognize people or places
- Worsening headache that won’t go away
- One pupil larger than the other
- Increasing drowsiness or inability to stay awake
- Slurred speech, weakness, or numbness
- Unusual behavior, increasing confusion, or agitation
These signs can indicate bleeding or swelling in the brain, which requires immediate treatment. They can appear right after the injury or develop over the following hours, which is why ongoing observation matters.
Returning to Normal Activity
Recovery from a concussion follows a gradual, step-by-step process. The CDC outlines a six-step return-to-play progression for athletes, and the same general principle applies to anyone recovering from a concussion: you increase activity slowly, and you only move forward if symptoms don’t return.
The progression starts with a return to everyday activities like school or desk work. From there, the person adds light aerobic exercise (5 to 10 minutes of walking or stationary cycling), then moderate activity with more head and body movement, then heavier non-contact exercise, then full practice with contact, and finally competition or full normal activity. Each step takes a minimum of 24 hours. If symptoms come back at any stage, that’s a signal to stop, rest, and drop back to the previous step.
Pushing through concussion symptoms or returning to activity too quickly risks prolonging recovery or, in rare cases with repeated head impacts, causing serious brain injury. Most people recover within a few weeks, but some experience symptoms for months, particularly if they’ve had previous concussions.