Bleeding into the inner layer of the skin, also known as the dermis, causes a purpuric rash. Some factors may make a person more susceptible to purpuric rashes, for example, taking certain medications.
A person with a purpuric rash has raised red or purple spots similar to small bruises or blood spots, measuring
Purpuric rashes can be associated with low platelet levels. Doctors call this thrombocytopenic purpura.
This article discusses some causes of purpuric rashes.
A person with thrombocytopenia has a low platelet count. The following types of purpuric rash may develop due to thrombocytopenia:
Thrombotic thrombocytopenic purpura
People with thrombotic thrombocytopenic purpura (TTP) do not have enough of the enzyme ADAMTS13, which controls blood clotting. This means a person produces
Some people inherit two ADAMTS13 genes with a mutation, one from each parent. Changes to the ADAMTS13 gene can mean the enzyme it produces does not function properly. People with one copy of the mutated gene may not experience TTP-associated symptoms.
Other people develop TTP after having another condition. Doctors call this “acquired thrombotic thrombocytopenic purpura,” which is unrelated to issues with the ADAMTS13 gene. Instead, the body produces antibodies that cause the enzyme to malfunction.
Learn more about thrombocytopenia.
Immune thrombocytopenic purpura
Immune thrombocytopenic purpura (ITP) occurs when the body produces antibodies against its own platelet or clotting factor membrane proteins.
Tissue macrophages — cells that destroy harmful organisms, such as bacteria — then clear the platelets covered in antibodies
Another theory is that ITP occurs due to cytotoxic T cells, a type of immune cell that directly kills germs, attacking the cells that produce platelets in the bone marrow. However, more research is necessary to understand this potential mechanism fully.
Learn more about immune thrombocytopenia.
Some people develop a purpuric rash in response to an infection. Also, some infections may affect platelet levels in the body.
For example, a tick bite
Purpura associated with systemic lupus erythematosus
Systemic lupus erythematosus (SLE) is an autoimmune condition, meaning a person’s immune system
People with SLE can experience purpuric rashes as a symptom of the condition. A 2020 study reported blood vessel inflammation in the small vessels of the skin as a feature of SLE. This resulted in lesions, such as purpura.
A person with nonthrombocytopenic purpura has platelet counts within the typical range. This means the cause of the rash is likely for other reasons, including:
Doctors do not know the exact cause of Henoch Schönlein purpura. However, it could occur due to inflammation of the blood vessels, also known as vasculitis. It is the most common type of vasculitis in children in North America.
Some people develop Henoch Schönlein purpura following an upper respiratory tract infection or cold. It causes the immune system to attack blood vessels in the skin, intestines, joints, and kidneys. A person bleeds into their skin through their inflamed blood vessel walls.
Learn more Henoch-Schönlein purpura.
Ehlers-Danlos syndromes refer to inherited conditions affecting the connective tissues. Connective tissue supports various structures in the body, including the:
- blood vessels
People with the vascular form of Ehlers-Danlos syndrome have skin that bruises very easily. This is because their blood vessels can split open. The person’s skin may also be so thin that small blood vessels are visible, especially on the upper chest and legs.
There is a risk of internal bleeding with the vascular form, which could become life threatening. For this reason, doctors often consider it the most serious form of the condition.
Learn more about Ehlers-Danlos syndrome.
- backs of the hands
Doctors refer to this as actinic purpura. It happens because sun exposure can worsen skin thinning and blood vessel fragility that naturally accompanies the reduction in collagen as a person ages.
Learn more about actinic purpura in older people.
Vitamin C deficiency
Scurvy can cause a purpuric rash. A lack of vitamin C can cause problems with collagen synthesis, the cause of most signs of scurvy.
Medications to treat other medical conditions can also lead to thrombocytopenic and nonthrombocytopenic purpura. This may be because some medications can affect platelet counts while others are less likely to.
Although many different drugs have an association with thrombocytopenia, drug-induced thrombocytopenia is most common with heparin, according to a 2018 review. Heparin is an anticoagulant that doctors use to prevent potentially dangerous clotting of blood.
A purpuric rash appears as red or purple spots on the skin that do not go away when a person presses glass against it. The rash appears because of bleeding from blood vessels into the second layer of skin, known as the dermis.
Causes of a purpuric rash can vary according to the type a person has, as well as other factors such as their health status, genetic makeup, current medications, and co-occurring conditions.