Why do I bruise easily? Usually fragile skin and blood thinners, not a blood disorder

For most adults who notice they bruise more easily than they used to, the cause is not a blood disorder but the skin itself: with age, sun exposure and some medicines, the skin thins and its small blood vessels lose their support, so a minor knock that once did nothing now tears a vessel and leaves a mark [s1]. Added on top, the low-dose aspirin and anticoagulants that many older people take make any bleeding — including into the skin — more likely [s3].

That covers the large majority of easy bruising. A smaller set of patterns points somewhere that does need a doctor, and the difference is worth knowing.

The skin story

Dermatologists have a name for the age-related loss of the skin's protective mechanical strength: dermatoporosis, a chronic cutaneous fragility syndrome [s1]. Its early, "rather trivial" markers are exactly the things people report as easy bruising — senile purpura (the flat, purple blotches that appear on the backs of ageing forearms and hands), star-shaped white pseudo-scars, and visible skin thinning [s1]. The mechanism is a breakdown in the skin's structural matrix, in which the hyaluronate–CD44 system that maintains the tissue's elasticity fails, leaving vessels poorly cushioned [s1]. In its more advanced form the same fragility produces skin that lacerates from minor trauma, heals slowly, and can bleed beneath the surface into large spreading haematomas serious enough to need hospital care — which is why the authors argue it should be prevented and treated, like osteoporosis, rather than dismissed as cosmetic [s1]. The biggest modifiable contributor is a lifetime of sun; the evidence on what actually protects skin is weighed in our piece on supplements for photoageing.

Steroids thin the skin — including inhalers

Corticosteroids accelerate the same process, and not only the tablets. A cross-sectional study of 68 patients compared skin in people on long-term oral prednisolone, high-dose inhaled steroids, low-dose inhaled steroids and controls [s2]. Both the oral-steroid group and the high-dose inhaler group had significantly thinner skin at every site measured — 28–33% thinner than controls on oral prednisolone, and 15–19% thinner on high-dose inhalers [s2]. Purpura followed the same line: it was present in 12 of 15 patients on oral prednisolone and 10 of 21 on high-dose inhalers, against just 2 of 17 controls, while low-dose inhalers made little difference [s2]. The finding that an inhaled drug, taken for the lungs, visibly weakens the skin is a reminder that "easy bruising" often has a nameable, dose-related cause sitting in the medicine cabinet.

The blood-thinning tax

Antiplatelet and anticoagulant drugs do their job by making clotting slower, and the trade-off is more bleeding, bruises included. The scale of it in otherwise healthy older people was measured by ASPREE, which randomised 19,114 community-dwelling adults aged 70 or over (65 and over for US black and Hispanic participants) with no cardiovascular disease to 100 mg of enteric-coated aspirin or placebo [s3]. Over a median of 4.7 years, major haemorrhage occurred at 8.6 events per 1,000 person-years on aspirin versus 6.2 on placebo — a 38% relative increase (hazard ratio 1.38; 95% CI 1.18 to 1.62; P<0.001) — without a matching drop in cardiovascular events [s3]. That is major bleeding; the far commoner, minor consequence is exactly the everyday bruising people notice. The same logic applies more strongly to the anticoagulants used for conditions such as atrial fibrillation, covered in our report on anticoagulation decisions. It is also why the old habit of taking a daily aspirin "just in case" has been re-examined in healthy older adults, where ASPREE found the bleeding cost without a matching cardiovascular payoff — the subject of our piece on aspirin in healthy ageing [s3]. None of this is a reason to stop a prescribed drug, which is a decision for the prescriber.

These causes stack. The person who bruises most easily is often older, has decades of sun exposure, uses an inhaled or oral steroid, and takes an antiplatelet or anticoagulant — each thinning the skin or slowing clotting a little, and together turning an unremarkable knock into a visible mark [s1][s2][s3]. What separates ordinary age-related bruising from a new problem is usually the change against that stable background, not the bruising itself.

When bruising is not the skin

A different picture calls for assessment rather than reassurance. Bruises that appear with no remembered injury, that come with pinpoint red or purple spots (petechiae), that arrive suddenly and in numbers, or that accompany bleeding from the gums, nose, urine or stool, are not the same problem as fragile forearms, because they can reflect a low platelet count or a clotting disorder. So is easy bruising in a child, or a new pattern with fevers, weight loss or bone pain. These are reasons to see a doctor rather than to reach for vitamin C or "vein-strengthening" supplements, for which the marketing runs well ahead of the evidence. This article is informational and is not medical advice.

Sources

• Dermatoporosis: A Chronic Cutaneous Insufficiency/Fragility Syndrome — Dermatology, 2007-10-02
• Purpura and dermal thinning associated with high dose inhaled corticosteroids — BMJ, 1990-06-16
• Effect of Aspirin on Cardiovascular Events and Bleeding in the Healthy Elderly — New England Journal of Medicine, 2018-09-16