A rash is a change in skin appearance, texture, or color. Observing how a rash reacts to pressure provides important clues for healthcare professionals. This characteristic, known as “blanching,” helps differentiate various skin conditions and guides diagnostic decisions.
Understanding Blanching Rashes
A blanching rash temporarily disappears or fades when pressure is applied. The skin returns to its original reddish appearance once pressure is released. This occurs because redness is due to blood vessels near the skin’s surface being filled with blood (vasodilation). When pressure is applied, blood is temporarily pushed out of these dilated capillaries, causing the skin to lighten.
To check for blanching, gently press a clear drinking glass firmly onto the rash. Observe if the rash disappears or turns pale through the glass and then reappears when the glass is lifted. If the rash consistently fades under pressure, it indicates blanching.
Blanching rashes are often associated with increased blood flow or temporarily dilated vessels. Common examples include heat rashes from blocked sweat ducts, or allergic reactions like hives (urticaria) where histamine release dilates blood vessels. Viral rashes, such as those seen in measles or roseola, also blanch because redness stems from inflammation and increased capillary blood flow rather than blood leakage. These rashes, while potentially uncomfortable, are generally less concerning than non-blanching rashes.
Understanding Non-Blanching Rashes
In contrast to blanching rashes, a non-blanching rash does not fade when pressure is applied. The red or purple spots remain visible even with firm pressure. This indicates the redness is not from blood within vessels, but from blood that has leaked out of capillaries into surrounding skin tissue. This leakage is medically termed extravasation.
Non-blanching rashes vary by the size of leaked blood spots. Small, pinpoint red or purple spots, less than 3 millimeters, are petechiae. Larger patches, 3 to 10 millimeters, are purpura. Both signify bleeding under the skin.
Non-blanching rashes indicate potentially serious underlying conditions requiring urgent medical attention. For instance, meningococcal septicemia, a severe bacterial infection, commonly presents with a non-blanching rash. The rash in meningitis can sometimes begin as blanching but rapidly progresses to non-blanching as blood leaks. Other causes include certain blood disorders with impaired clotting, or conditions like Henoch-Schönlein purpura, involving small blood vessel inflammation.
When to Seek Medical Attention
Any non-blanching rash should be considered a medical emergency. Seek immediate medical evaluation, especially if it appears suddenly or spreads rapidly. Such rashes can signal severe infections like meningococcal disease or sepsis, which can progress quickly and become life-threatening.
Accompanying symptoms heighten the need for immediate medical attention. If a non-blanching rash is present with fever, stiff neck, severe headache, confusion, unusual drowsiness, light sensitivity, vomiting, or difficulty breathing, urgent medical care is necessary. These combined symptoms suggest a condition requiring prompt diagnosis and treatment.
While non-blanching rashes require urgent response, even blanching rashes may warrant a doctor’s visit. If a blanching rash is widespread, intensely itchy, painful, or accompanied by concerning symptoms like difficulty breathing or swelling, medical consultation is advisable. Any rash causing significant discomfort or concern should be evaluated by a healthcare provider.