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Petechiae develop when blood leaks from the smallest vessels into the tissue — because the pressure inside them briefly rises too sharply, because platelets are lacking or not working properly, or because the vessel wall is inflamed. As a rough rule of thumb: dots point more towards a problem with the platelets, larger flat bruises more towards one with the clotting factors. Larger patches are covered in the article on bruising for no reason.
Violent coughing, vomiting, straining hard on the toilet or during childbirth, heavy lifting while holding your breath: in all of these, the pressure in the veins of the head and neck rises sharply for a few seconds, and the finest vessels give way. The dots then appear on the face, around the eyes and on the neck — but not further down. Dots on the arm below a tight blood pressure cuff or under tight straps develop in exactly the same way. A bright red patch in the white of the eye after a coughing fit (subconjunctival haemorrhage) usually belongs in this harmless group too. Everything fades within a few days. The crucial point: the distribution has to fit the trigger. If after vomiting there are also dots on the legs or abdomen, that explanation is not enough.
Healthy adults have around 150,000 to 400,000 platelets per microlitre; the reference ranges vary slightly from laboratory to laboratory. Slightly low counts usually cause no symptoms; spontaneous petechiae generally only appear at considerably lower counts — first on the lower legs and feet, and in the lining of the mouth. Blood blisters in the mouth, bleeding gums and nosebleeds that are hard to stop are regarded as signs of a more pronounced bleeding tendency.
Common causes include immune thrombocytopenia (ITP), in which the immune system breaks down the body's own platelets — in children often weeks after a viral infection and frequently self-limiting, in adults more often chronic — as well as viral infections, an enlarged spleen in liver disease, medicines, marked vitamin B12 or folic acid deficiency, heavy drinking and, rarely, diseases of the bone marrow. Not every low count is real: if the platelets clump together in the EDTA tube, the analyser counts too few. This harmless pseudothrombocytopenia is cleared up by a repeat count in citrated blood.
Sometimes the number is right, but the platelets stick together less well. The most common reason is medicines such as aspirin and classic painkillers. The main congenital cause is von Willebrand disease, the most common inherited bleeding disorder — it tends to show itself through nosebleeds, bleeding after dental treatment and heavy periods rather than through petechiae. Advanced chronic kidney disease can also disrupt platelet function.
If the small vessels are inflamed, the dots and patches feel slightly raised (palpable purpura). In children, IgA vasculitis (formerly Henoch–Schönlein purpura) is the most common form: often after a respiratory infection, with patches on the legs and buttocks, joint pain and abdominal pain. Because the kidneys can be affected too, the urine is monitored over several weeks. In adults, infections or medicines are more often behind it.
Many viral infections bring the odd petechia with them, which disappears along with the infection. Fine pinpoint bleeds on the palate are typical of scarlet fever and glandular fever. After a trip to the tropics, a fever with petechiae can point to dengue fever — in that case avoid aspirin and ibuprofen until the cause has been clarified. The most dangerous combination is meningococcal blood poisoning (sepsis): a high fever, a rapidly worsening feeling of being unwell and spots that cannot be pressed away and quickly multiply. In children and adults alike, it can become life-threatening within a few hours.
With weak veins, tiny bleeds occur on the lower legs over years and stain the skin rust-brown; the orange-brown pinpoints of capillaritis look similar and are harmless. More on this under heavy legs. In older age and on cortisone, the skin becomes thin — the flat purple patches on the forearms are larger than petechiae but are often mistaken for them. Rare, but real, is vitamin C deficiency (scurvy) with a very one-sided diet or alcohol dependence: petechiae around the hair follicles, corkscrew hairs, bleeding gums.
Petechiae can be an early sign of leukaemia. Isolated dots without any other symptoms do not point to it. What should make you sit up and take notice, however, is the combination with unusual tiredness, pallor, frequent infections, unexplained fever, night sweats, bone pain or swollen lymph nodes — in that case have a blood count done promptly.
These observations do not replace a diagnosis. But they help you judge how urgent things are, and they make the conversation at the practice more precise.
Without warning signs, the assessment works from the simple to the more elaborate. It is the cause that is treated, not the dots.
Medicines are among the most common causes — and among the easiest to put right. They slow down platelet function, lower the platelet count or trigger inflammation of the vessels.
Aspirin and clopidogrel — like prasugrel and ticagrelor — are meant to prevent blood vessels from becoming blocked. The downside: bruises, nosebleeds, prolonged bleeding and occasionally fine petechiae. With aspirin, the effect on a platelet lasts for that platelet's whole lifespan of around seven to ten days. An unusual number of new dots or bleeding from the mucous membranes is not to be expected — in that case the practice checks whether the platelet count has fallen or an interaction is behind it. Anticoagulants such as phenprocoumon, apixaban or rivaroxaban, on the other hand, tend to cause larger flat bruises; lots of petechiae while taking them are a reason to check the platelets.
Heparin injections can, rarely, trigger heparin-induced thrombocytopenia (HIT), typically five to ten days after starting. The treacherous part: despite the falling platelet count, the main danger is thrombosis. A swollen leg, shortness of breath or painful dark areas at the injection sites need to be checked immediately.
Via the immune system, platelets are lowered by quinine (prescribed for night-time calf cramps), for example, by antibiotics such as co-trimoxazole or vancomycin and by antiepileptics such as carbamazepine; with valproic acid and linezolid it depends more on the dose or the duration. Blood cell production is slowed by methotrexate, azathioprine and many cancer medicines. With methotrexate, accidentally taking it daily instead of weekly is a known and dangerous mistake — warning signs are a sore lining of the mouth, bleeding and petechiae.
SSRIs such as sertraline or citalopram lower the serotonin content of the platelets; together with aspirin, ibuprofen or anticoagulants, the risk of bleeding rises. Ginkgo, high-dose omega-3 fatty acids and vitamin E are also linked with a tendency to bleed — the evidence is limited, and it matters mainly in combination (more in the guide on herbal medicines). Long-term cortisone makes the skin thin and fragile. In addition, some antibiotics, painkillers and diuretics can trigger an allergic inflammation of the vessels with palpable dots on the lower legs around one to three weeks after starting.
Aspirin, ibuprofen, diclofenac and naproxen additionally inhibit the platelets. Paracetamol hardly affects them at usual doses and is often regarded as the better-tolerated option here, but because of the liver it has a fixed maximum daily dose. According to the package leaflet, over-the-counter painkillers should only be taken for a few days in a row without medical advice, usually no longer than three to four days. The best way to settle the choice is with your practice or pharmacy.
Documented with dates, you can see the link in time at a glance.
You cannot prevent ITP or an infection — but you can avoid some of the triggers.
The interaction check shows which combinations increase the tendency to bleed.
This article is for general information and does not replace medical advice, diagnosis or treatment. The self-tests described — including the glass test — are a guide and not a diagnosis. If you have petechiae with a fever and feeling unwell, bleeding into the skin that spreads rapidly, bleeding from the mucous membranes, or blood in your urine or stools, please contact a doctor or the emergency services without delay.
