A rash represents a change in the skin’s appearance, including alterations in texture and color. Observing how a rash reacts to pressure, known as “blanching,” offers valuable insights into its nature. This simple observation helps differentiate between various types of rashes.
Understanding Blanching: What It Is and How to Check
Blanching refers to the temporary fading of redness in a rash when light pressure is applied, with the color returning once the pressure is released. This indicates the redness is primarily due to dilated blood vessels near the skin surface. The color change occurs because the applied pressure temporarily pushes blood out of these vessels.
To check if a rash blanches, gently press a finger or clear glass firmly against the reddened area. Observe if the color lightens or turns pale under pressure. The redness should quickly return when pressure is removed. On darker skin tones, the rash might not turn white, but the discoloration will temporarily lessen or disappear.
The Science Behind Blanching
The reason some rashes blanch while others do not lies in the state of blood vessels. Blanching occurs when redness is caused by increased blood flow within superficial blood vessels. When pressure is applied, blood within these dilated vessels is temporarily pushed away, causing the skin to lighten. Once pressure is released, blood rapidly refills the vessels, and the redness reappears.
In contrast, non-blanching rashes occur when redness results from blood that has leaked out of blood vessels into the surrounding skin tissue. This extravasated blood, no longer contained within vessels, cannot be pushed away by pressure. Therefore, pressing on a non-blanching rash will not cause it to fade. This indicates bleeding under the skin, such as in petechiae or purpura.
Interpreting Blanching: What It Indicates
The ability of a rash to blanch offers a diagnostic distinction regarding its underlying cause. Blanching rashes are associated with conditions where increased blood flow or inflammation is present. This includes common inflammatory skin disorders such as hives, eczema, and rosacea. Viral rashes, like those seen in measles, also blanch. Allergic reactions often result in blanching rashes.
A non-blanching rash suggests bleeding into the skin. These rashes, appearing as tiny pinpoint spots (petechiae) or larger bruise-like areas (purpura), do not fade under pressure. While some are benign, like those from forceful coughing or vomiting, they can signal more serious conditions such as vasculitis, autoimmune disorders, or blood clotting issues.
When to Consult a Healthcare Professional
Consult a healthcare professional for any concerning rash, particularly if it does not blanch. A non-blanching rash, especially if accompanied by other symptoms, warrants immediate medical attention. These symptoms include fever, a stiff neck, severe headache, confusion, difficulty breathing, or extreme pain. Such combinations indicate serious conditions like meningitis or sepsis.
Also consult a healthcare professional for any rash that spreads rapidly, is painful, develops blisters, or affects sensitive areas like the eyes, mouth, or genitals. Rashes accompanied by systemic symptoms such as persistent fever, fatigue, or joint pain also require evaluation.