She noticed the first bruise on a Tuesday morning — a dark, plum-colored patch on her upper arm that she could not explain. By the end of the second week, there were five more: two on her thighs, one on her shin, another near her ribs. She lived alone. She had not fallen. She had no memory of bumping into anything. The marks just kept showing up.
Her story, shared in an online health forum, is not unusual. Doctors who treat blood disorders and sleep conditions say unexplained bruising is one of the most common reasons patients book same-day appointments — and one of the most commonly dismissed. The causes range from restless sleep and medication side effects to nutritional deficiencies and, less often, serious blood disorders. What matters, specialists say, is whether someone treats recurring bruises as a question worth answering.
Bruising in your sleep is more common than most people realize
One of the most straightforward explanations is also the hardest to catch: the injury happens while you are unconscious. During certain sleep stages, some people thrash, kick, or roll forcefully enough to strike a headboard, wall, or nightstand, breaking small blood vessels beneath the skin. They wake up with bruises and no memory of the impact.
When these movements are frequent and violent, they may point to REM sleep behavior disorder (RBD), a condition in which the normal muscle paralysis that occurs during REM sleep is incomplete. People with RBD physically act out dreams — punching, flailing, even leaping from bed. The Mayo Clinic notes that RBD can cause self-injury or injury to a bed partner and is more common in men over 50, though it can affect anyone. It is also associated with neurodegenerative conditions such as Parkinson’s disease, which makes diagnosis important beyond just explaining the bruises.
Even without a formal sleep disorder, stress, caffeine, and alcohol close to bedtime can make sleep more restless and increase the chance of nighttime collisions with furniture. For someone who lives alone, there is no witness to confirm what happened — which is exactly why the bruises feel so unsettling.
When bruising signals a problem with blood or vessels
Not all unexplained bruises trace back to the bedroom. When bruises appear frequently, grow unusually large, or show up in places that rarely take impact — the trunk, neck, or face — physicians start thinking about what is happening inside the blood itself.
A bruise forms when small blood vessels called capillaries rupture and leak blood into surrounding tissue. Normally, platelets and clotting proteins seal the break quickly. But when platelet counts are low (a condition called thrombocytopenia), when clotting factors are deficient, or when vessel walls are unusually fragile, bruises form more easily and from less force.
The Mayo Clinic’s guide on easy bruising notes that people should contact a healthcare professional if they experience bruises that are large, painful, or appear frequently without known cause — especially if accompanied by unusual bleeding from the gums or nose, or tiny red or purple dots (petechiae) that do not blanch when pressed.
The Columbia Doctors symptom library adds that sudden unexplained bruising or a noticeable increase in bruising frequency can indicate a serious underlying condition and warrants medical evaluation.
The medicine cabinet and the dinner plate
Before assuming the worst, it is worth checking two places most people overlook: the bathroom shelf and the refrigerator.
Blood thinners such as warfarin and direct oral anticoagulants (DOACs) are well-known culprits, but they are far from the only medications that affect clotting. Healthline’s review of random bruising causes lists nonsteroidal anti-inflammatory drugs (ibuprofen, naproxen), certain antidepressants (particularly SSRIs), and even fish oil supplements as agents that can lower the threshold for visible bruising. In these cases, the bruise is not truly “unexplained” — the person simply did not connect a minor bump to a medication that made the bump matter more.
Nutritional gaps can produce a similar effect. Vitamin C is essential for collagen production, which keeps blood vessel walls strong; a deficiency weakens those walls and leads to easier rupture. Vitamin K plays a direct role in the clotting cascade, and low levels impair the body’s ability to stop even small bleeds beneath the skin. The Mayo Clinic and Everyday Health both identify these deficiencies as contributors to easy bruising, and both note that a simple blood test can confirm or rule them out.
Age matters more than most people expect
One factor that often goes unmentioned in these conversations is aging itself. As people get older — particularly after 60 — the skin thins, loses subcutaneous fat, and provides less cushioning for the capillaries beneath it. The blood vessels themselves become more fragile. The result is a condition sometimes called senile purpura (or actinic purpura), in which dark, blotchy bruises appear on the forearms and hands after minimal contact.
The Mayo Clinic explains that years of sun exposure accelerate this process by breaking down collagen and elastin in the skin. While senile purpura is not dangerous on its own, it can make it harder to distinguish age-related bruising from bruising caused by a blood disorder — another reason to bring the pattern to a doctor rather than assume it is “just getting older.”
How doctors read a bruise
Physicians do not just count bruises. They assess location, size, pattern, and timing.
The UK’s National Institute for Health and Care Excellence (NICE) instructs clinicians to distinguish between bruises on bony prominences — shins, knees, forearms — which are common and usually benign, and bruises on protected or soft-tissue areas such as the trunk, neck, ears, or inner arms, which raise concern for medical conditions or, in some cases, abuse.
In pediatric medicine, this logic has been formalized into the TEN-4-FACESp clinical decision rule, which flags bruises on the torso, ears, and neck in children under four as indicators that should prompt further investigation. While the rule was designed for pediatric patients, the underlying principle — that bruise location matters as much as bruise frequency — applies across age groups.
A doctor evaluating unexplained bruising will typically order a complete blood count (CBC) to check platelet levels, along with coagulation studies (PT/INR and PTT) to assess clotting function. If those come back normal, the investigation may expand to liver function tests, vitamin levels, or referral to a hematologist.
What to do before the appointment
For anyone tracking unexplained bruises, documentation makes a real difference. Photograph each new bruise with a ruler or coin for scale, note the date it appeared, and record how long it takes to fade. Write down any medications, supplements, and major dietary changes from the preceding weeks. This kind of timeline gives a clinician far more to work with than a vague report of “bruising a lot lately.”
The Cleveland Clinic’s bruise overview notes that most bruises heal within two to four weeks without treatment. But bruises that linger beyond that window, keep recurring in clusters, or appear alongside other bleeding symptoms — nosebleeds, heavy menstrual periods, blood in urine or stool — should prompt a visit sooner rather than later.
Healthline’s guide on persistent bruises adds that a doctor may measure blood-clotting time and screen for platelet disorders if bruising is frequent or slow to resolve.
The bottom line
For the woman who spent two weeks cataloging bruises she could not explain, the answer could be as mundane as a restless sleep habit or an ibuprofen regimen she stopped thinking about months ago. Or it could be the first visible sign of a blood disorder that is easier to treat when caught early. The only way to know is to stop treating the bruises as a mystery and start treating them as medical information.
Anyone experiencing frequent unexplained bruising should bring it up with a primary care provider. For those without an established doctor, tools such as Healthline’s provider finder or a local urgent care clinic can serve as a starting point. The bruises are already telling a story. The next step is making sure someone qualified is reading it.
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