Easy bruising is usually not caused by illness. In most adults it comes down to thinning skin, which leaves the small vessels underneath less protected. Even so, seven causes do leave traces in your blood, and those are the ones almost nobody writes about.
We think that is a missed opportunity. Nearly every article on this topic stops at "your skin gets thinner". Which value might say something about it is left out entirely.
Below are seven causes. For each one you will read which blood value may offer insight, and when it is worth raising with your GP.
Easy bruising: the 7 causes in short
A bruise forms when small vessels under the skin tear and blood leaks into the tissue. How easily that happens depends on your skin, your platelets, your clotting and your medication. These seven causes explain most of what people notice.
| Cause | Blood value that may offer insight |
|---|---|
| 1. Skin thinning with age | None, this shows on the skin itself |
| 2. Blood thinners, aspirin and NSAIDs | PT (prothrombin time) and INR |
| 3. Long-term corticosteroid use | No direct value, but your medication list |
| 4. Low platelet count | Platelets in the complete blood count |
| 5. Inherited clotting disorder | APTT and von Willebrand factor |
| 6. Reduced liver function | ALT, AST, GGT and PT |
| 7. Vitamin C deficiency | Vitamin C |
A bruise after a needle in your arm is a different matter. It has an obvious cause and does not belong on this list. That one is covered in bruise after a blood draw.
1. Your skin thins with age
The most common cause of easy bruising is ageing. Skin and the fat beneath it get thinner, so the vessels underneath sit closer to the surface. Doctors call this actinic purpura. You will usually see it on the forearms and the backs of the hands, exactly where the sun has been landing for decades.
Dermatologist Roger Ceilley described in 2017 that it becomes more common with advancing age (PMID 28979656). Sun damage speeds it up, because UV light breaks down collagen.
These patches are usually painless. They do fade more slowly than an ordinary knock.
2. Blood thinners, aspirin and anti-inflammatories
Medication is the second big explanation. Anticoagulants such as acenocoumarol or a DOAC slow your clotting. Aspirin and NSAIDs such as ibuprofen and diclofenac make platelets less sticky. The effect is the same: a small knock keeps leaking for longer.
The Dutch Farmacotherapeutisch Kompas lists bruising and bleeding as a known side effect of these drugs. With vitamin K antagonists, the prothrombin time or INR shows how far your clotting is extended.
Never stop a blood thinner on your own. Talk it through with your GP or your anticoagulation clinic.
3. Long-term corticosteroid use
Corticosteroids thin the skin when used over long periods. That applies to tablets, but also to strong creams and even to high-dose inhalers. Capewell and colleagues described purpura and thin skin in the BMJ back in 1990, in people using high doses of inhaled corticosteroids (PMID 2372620).
Recognise the pattern? Bruises on the forearms in someone who has been using inhalers or prednisone for years.
No blood value points to this. Your medication list does.
4. A low platelet count
Platelets seal small tears in your vessel walls. When there are too few, such a tear keeps leaking for longer. This is the first cause on the list you can see directly in your blood, because platelets are part of every complete blood count.
A reduced count can have many causes, from a recent viral infection to medication. On its own it says nothing about any specific condition.
There is more background in platelets: normal values, high and low explained.
5. An inherited clotting disorder such as von Willebrand
Some people produce less effective clotting proteins from birth. Von Willebrand disease is the best known of them. And it turns up more often than most people assume.
Rodeghiero and colleagues tested 1,218 schoolchildren and found von Willebrand in 10 of them, which is 0.82 percent (PMID 3492222). That is roughly 1 in 120.
The pattern is usually recognisable: bruising since childhood, prolonged bleeding after a dental visit, and heavy periods. An APTT and the von Willebrand factor may offer insight here.
6. Your liver makes almost all your clotting factors
Few people know about this link. Your liver produces most of your clotting factors. When the liver works less well, that production drops. Clotting then takes longer.
This is the cause I see missed most often. People will happily get their liver checked after a heavy stretch. They just never connect it to the bruising.
ALT, AST and GGT show how your liver is doing. The prothrombin time says something about the clotting itself. With heavy alcohol use, those two can stand out together.
The value-by-value explanation is in liver values explained: ALT, AST and GGT.
7. A vitamin C deficiency
Vitamin C is needed to build collagen, and collagen keeps your vessel walls firm. With a serious deficiency those walls become more fragile. Small bleeds then appear around the hair follicles, often on the thighs.
Nguyen and colleagues described this in 2003 as a picture you can recognise on the skin (PMID 12581082). True scurvy is rare in the Netherlands. The Dutch Voedingscentrum points out that vegetables and fruit supply plenty of vitamin C.
Not sure? Vitamin C deficiency: symptoms and when measuring makes sense goes into more detail.
Which disease causes bruising?
There is no single disease that causes bruising. Conditions that affect your clotting or your platelet count can produce it, such as von Willebrand, a liver condition, or a shortage of platelets. In the large majority of cases, though, the cause sits with skin, age or medication.
Bruises on their own are therefore a weak signal. The pattern around them says more: where they appear, how often, and whether other bleeding comes with them.
What strikes me here is that people reach for a disease first. More often the answer sits in the medicine cabinet.
Do women bruise more easily than men?
Often yes, but the reason is more nuanced than it is usually presented. Women on average have a different distribution of subcutaneous fat and slightly thinner skin, so vessels get pinched more easily. For actinic purpura, the age-related form from point 1, that difference does not apply.
Ceilley writes that actinic purpura occurs with equal frequency in men and women (PMID 28979656). So the common claim that women always bruise faster does not hold for every form.
How long does a bruise take to fade?
Most bruises clear within two weeks. The colour shifts along the way from red to purple, then green and finally yellow-brown, as your body breaks down the haemoglobin. In older people and in those using blood thinners it often takes longer.
A patch that is unchanged after three to four weeks, or that keeps growing, belongs with your GP.
When do you raise bruising with your GP?
In short: when the pattern changes, or when other bleeding joins it. The Dutch patient portal Thuisarts describes bruising without a clear cause as a reason to contact your GP. New symptoms alongside the patches are also worth discussing.
Signals people typically raise with their GP:
- Patches that appear without you having knocked into anything
- Frequent nosebleeds, or prolonged bleeding from a small cut
- Periods that are far heavier than you are used to
- Small red dots on the skin that do not fade when you press on them
- Bruising together with fever, bone pain or unusual fatigue
American primary care literature puts it the same way: the patient history determines whether blood testing is useful, not the bruise itself (PMID 26926815 and PMID 39556633).
Which blood values give insight into easy bruising?
Four values come up most often: platelets, the prothrombin time, the liver values and vitamin C. Together they cover clotting, the production of clotting factors, and the firmness of your vessel walls. They do not produce a diagnosis, but they do give your GP something concrete to work from.
Take two people aged 58 with the same patches on their forearms. In one, platelets read 240 and the liver values are normal, and the picture fits thinning skin. In the other, platelets read 95, and the conversation with the GP becomes a different conversation straight away.
What a standard blood count contains is set out in the complete blood count explained. The individual value sits on the platelets page. How to read a result is covered in understanding your blood test results.
Anyone who wants clotting looked at as a whole can consider the complete coagulation panel. Discuss the result with your GP afterwards.
What I make of it
Having read through what is published on this topic, what strikes me most is how quickly it gets filed away as a skin matter. That is often right. But not always. The difference sits in the pattern rather than in any single patch.
So over the next two weeks, note where patches appear and whether you knocked into something. Take that list to your GP if any of them showed up without a cause.
References
- Neutze D, Roque J. Clinical evaluation of bleeding and bruising in primary care. American Family Physician, 2016. PMID 26926815
- Hughes PR, Lewis MN, Adams SS. Bleeding and bruising: primary care evaluation. American Family Physician, 2024. PMID 39556633
- Rodeghiero F, Castaman G, Dini E. Epidemiological investigation of the prevalence of von Willebrand disease. Blood, 1987. PMID 3492222
- Ceilley RI. Treatment of actinic purpura. Journal of Clinical and Aesthetic Dermatology, 2017. PMID 28979656
- Capewell S, Reynolds S, Shuttleworth D, Edwards C, Finlay AY. Purpura and dermal thinning associated with high dose inhaled corticosteroids. BMJ, 1990. PMID 2372620
- Nguyen RT, Cowley DM, Muir JB. Scurvy: a cutaneous clinical diagnosis. Australasian Journal of Dermatology, 2003. PMID 12581082
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
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