Eczema, also known as atopic dermatitis, is a chronic inflammatory skin condition that causes intense itching, dryness, and the appearance of rashes. The condition is characterized by a compromised skin barrier, which makes the skin more sensitive to environmental triggers and prone to inflammation. Understanding how an eczema rash behaves under pressure is helpful for distinguishing it from other types of skin eruptions. This physical observation, known as blanching, offers a simple way to assess the underlying cause of the redness.
Understanding Skin Blanching
The term “blanching” describes a temporary lightening or whitening of the skin that occurs when external pressure is applied to a reddened area. This diagnostic technique, often called diascopy, is performed by pressing a clear glass slide or a fingertip firmly against the rash. The pressure temporarily forces blood out of the superficial capillaries in that localized area.
If the redness disappears under pressure and quickly returns once the pressure is released, the rash is considered blanching. This reaction indicates that the color is due to blood contained within the blood vessels, a condition known as erythema. The purpose of this test is to differentiate rashes caused by vascular dilation from those caused by blood leakage into the surrounding tissue.
How Eczema Reacts to Pressure
Eczema rashes typically blanch when pressure is applied. The redness associated with an active eczema flare-up is a direct result of inflammation. During this inflammatory response, the small blood vessels near the skin’s surface widen, a process called vasodilation, which increases blood flow to the affected area.
This increased blood volume causes the characteristic redness seen in eczema lesions, which may vary in color depending on skin tone. When the skin is pressed, this extra blood is displaced from the dilated vessels, causing the area to temporarily turn pale. The ability to blanch confirms the blood causing the discoloration remains inside the vessels. A unique feature sometimes noted in eczema is a “delayed blanch response,” where the whitening may last longer than in other inflammatory conditions.
Distinguishing Eczema from Non-Blanching Rashes
The blanching test separates inflammatory rashes, like eczema, from hemorrhagic rashes. Rashes that do not blanch under pressure are known as non-blanching rashes. This indicates the redness is caused by blood that has leaked out of the capillaries and into the surrounding skin tissue (extravasated blood). This blood forms small spots called petechiae or larger patches called purpura, and cannot be pushed away by external pressure.
The failure to blanch is medically significant because it can signal underlying issues such as vasculitis, clotting disorders, or serious systemic infections. While a blanching rash suggests a less severe, localized inflammatory process, a non-blanching rash warrants urgent medical evaluation. A blanching rash points toward conditions like eczema or hives, while a non-blanching rash suggests a need for immediate investigation.
Key Visual Signs of Eczema
Beyond the blanching response, several other observable features help confirm an eczema diagnosis. The intense itching, or pruritus, is one of the hallmarks, often preceding the appearance of the rash itself. Visually, eczema patches frequently present with dryness and scaling, sometimes progressing to oozing and crusting during acute flares.
Chronic scratching leads to a thickening of the skin known as lichenification, which gives the skin a leathery appearance. Excoriations, or scratch marks, are also commonly seen on the affected areas. Eczema often follows specific distribution patterns, typically occurring in the folds of the elbows and knees, on the face and scalp in infants, and on the hands. A professional dermatological diagnosis remains the necessary next step after any at-home observation.