Purpura are small, flat blood spots on the skin that appear red, purple, or brown. They measure between 4 and 10 millimeters in diameter, roughly the size of a pencil eraser. Unlike a typical rash, purpura don’t fade when you press on them, which is the single most important visual feature that sets them apart.
Color on Different Skin Tones
The color of purpura depends heavily on your skin tone. On lighter complexions, the spots tend to look reddish-purple. On darker complexions, they appear brownish-black. This difference matters because purpura on dark skin can be harder to spot at first glance, especially if the spots are small. In both cases, the spots sit flat against the skin and don’t raise up or feel bumpy to the touch (with one important exception covered below).
How Purpura Differ From Petechiae and Bruises
Purpura sit in the middle of a size spectrum. Spots smaller than 4 millimeters are called petechiae, which look like tiny pinpoint dots, almost like someone flicked a red pen at your skin. Spots larger than 1 centimeter are classified as ecchymoses, which is essentially a bruise. All three are caused by blood leaking from small vessels under the skin, but size is how they’re categorized.
Purpura often appear as clusters of smaller dots grouped together in one area. Sometimes these clusters can look like a single larger patch, which is why people occasionally confuse them with bruises. The key difference: bruises usually result from a clear injury, while purpura can appear without any trauma at all.
The Glass Test
The simplest way to tell purpura apart from an ordinary rash is the glass test. Press a clear drinking glass firmly against the spots. If the marks remain visible through the glass and don’t fade under pressure, that’s a positive result pointing to purpura. A regular rash caused by dilated blood vessels will temporarily blanch (turn white or pale) when you press on it, then return to its color when you release. Purpura won’t do this because the blood has already leaked out of the vessels and is sitting in the surrounding tissue. No amount of pressure will push it back.
Flat vs. Raised Spots
Most purpura are completely flat. You can run your finger over them and feel no difference from the surrounding skin. However, some purpura are raised and bumpy, which is called palpable purpura. This raised texture signals that the blood vessels themselves are inflamed, a condition known as vasculitis. Palpable purpura look similar in color to flat purpura but feel like small, firm bumps when you touch them. This distinction is clinically significant because raised purpura point to a different set of underlying causes than flat ones.
How Purpura Change Over Time
Like bruises, purpura go through a predictable color shift as they heal. They typically start pinkish-red, then darken to deep blue or purple. Over the following days, they fade through violet, then green, then dark yellow, and finally pale yellow before disappearing. The full cycle takes roughly two weeks for most people, though this varies depending on the cause and whether new spots keep appearing.
If your purpura are healing through this normal color progression and no new spots are forming, that’s generally a reassuring sign. Purpura that keep spreading, increase in number, or appear alongside fever, joint pain, or unusual bleeding from the gums or nose suggest something more serious is going on and warrant prompt medical evaluation.
Where Purpura Tend to Appear
Purpura can show up anywhere on the body, but they’re most common on the lower legs, where gravity increases pressure on small blood vessels. They also frequently appear on the arms, torso, and buttocks. In older adults, purpura often develop on the forearms and backs of the hands, where the skin is thinner and blood vessels are more fragile. The location and pattern of the spots can give clues about the underlying cause. Purpura limited to the shins, for instance, suggest something different than purpura scattered across the trunk and limbs.
What Purpura Don’t Look Like
A few things are easy to confuse with purpura. Cherry angiomas are small, bright red bumps that are raised and don’t change color over time. Spider veins have a visible branching pattern. Hives are raised, itchy welts that move around and fade within hours. All of these blanch under pressure, which immediately rules out purpura. If you press a glass against the spots and the color disappears, what you’re seeing isn’t purpura, regardless of how similar the color looks at first glance.