Eczema, also known as atopic dermatitis, is a common inflammatory condition causing the skin to become red, dry, and intensely itchy. Identifying the cause of a skin rash often requires visual inspection and simple tests, such as applying pressure. The question of whether a rash blanches—temporarily fades with pressure—is a fundamental step in determining the underlying nature of the skin change. This pressure test helps differentiate between rashes caused by inflammation and those caused by bleeding under the skin.
Understanding Blanching and Vascular Reactions
Blanching is the temporary whitening or fading of a reddened area of skin when gentle pressure is applied. This physiological reaction occurs because pressure briefly pushes blood out of the superficial capillaries near the skin’s surface. When pressure is released, blood rapidly flows back, and the original color quickly returns. A rash that blanches indicates the redness is caused by vasodilation, meaning the blood vessels have widened but their walls remain intact. This is a normal inflammatory response where increased blood flow to the area is part of the body’s attempt to heal.
The Blanching Behavior of Eczema
Eczema lesions typically blanch when the skin is pressed. The redness associated with an eczema flare-up is primarily due to inflammation in the skin layers, which includes the widening of blood vessels in the superficial dermis. Since the blood remains contained inside these expanded vessels, external pressure temporarily displaces it, causing the rash to turn paler. This blanching response is expected because eczema, while inflammatory, does not typically involve the destruction of blood vessel walls or the leaking of red blood cells into the surrounding tissue. However, chronic, severe eczema often leads to thickened, leathery skin, a process called lichenification. Heavily thickened patches may sometimes blanch less distinctly or more slowly because these structural changes can affect circulation or the visibility of the underlying vessels.
Differentiating Eczema from Non-Blanching Rashes
The inability of a rash to blanch is a significant diagnostic signal because it suggests a much different, and often more serious, underlying cause. A non-blanching rash indicates that the discoloration is caused by blood that has leaked out of the capillaries and settled in the surrounding skin tissue, a phenomenon called extravasation. The absence of blanching is a sign that the blood vessels are damaged or that a systemic condition is causing bleeding under the skin. Rashes that do not blanch are commonly referred to as petechiae or purpura, depending on the size of the spots. Non-blanching rashes can be a symptom of severe conditions like vasculitis, septicemia, or meningitis, which require immediate medical attention.
Key Visual Cues for Eczema Confirmation
While a positive blanching test rules out certain serious conditions, it does not confirm eczema, as many common rashes also blanch. The diagnosis of atopic dermatitis relies on a combination of visual signs and symptoms. A primary characteristic is intense itching, or pruritus, which often precedes the visible rash and leads to scratching that worsens the condition. The rash typically presents as dry, scaly patches that can be red, pink, or on darker skin tones, shades of purple, brown, or ash gray.
Location and Chronicity
In infants and young children, eczema often appears on the cheeks and extensor surfaces of the limbs. In older children and adults, the rash commonly affects the flexural surfaces, such as the inside of the elbows and the back of the knees. Long-standing eczema results in thickened, leathery skin with enhanced skin markings. This chronic change is known as lichenification.