What does blanching of a rash indicate?

From the Guidelines

Blanching of a rash is a clinical sign that indicates the blood vessels under the skin are functioning normally and can temporarily empty when pressure is applied, which is a characteristic of certain rashes such as those seen in Rocky Mountain spotted fever (RMSF) 1. When you press on a blanching rash, it temporarily turns white or pale before returning to its original color once pressure is released. This occurs because the pressure pushes blood out of the small vessels in that area. Some key points to consider when evaluating a blanching rash include:

• The rash may appear as small, blanching, pink macules on the ankles, wrists, or forearms, and can spread to other areas of the body 1
• The presence or absence of a rash can be an important factor in diagnosing conditions such as RMSF, and a lack of rash should not preclude consideration of this diagnosis 1
• Non-blanching rashes, on the other hand, may indicate more serious conditions like petechiae or purpura, which can be associated with bleeding disorders, infections, or vasculitis To check for blanching, simply press a clear glass or your finger firmly against the rash for a few seconds and observe the color change, a test sometimes called the "glass test" which is particularly important for evaluating rashes in children with fever, as non-blanching rashes can sometimes signal serious infections requiring immediate medical attention. It's worth noting that while the study on cutaneous mastocytosis in children 1 provides information on various types of rashes and skin conditions, it does not specifically address the clinical significance of blanching rashes, and therefore the more recent and relevant study on RMSF 1 is given more weight in this assessment.

From the Research

Characteristics of Contact Dermatitis

• Contact dermatitis is a common inflammatory skin disease caused by exposure to contact allergens and irritants 2
• It can manifest as allergic contact dermatitis or irritant contact dermatitis, among other subtypes 2, 3
• The condition is characterized by pruritic and erythematous patches, and can be diagnosed through patch testing and other diagnostic tests 2, 4

Symptoms and Diagnosis

• Symptoms of contact dermatitis include local skin rash, itchiness, redness, swelling, and lesions 5
• Diagnosis is based on a thorough history, physical examination, and patch testing 4
• The patch test is a crucial diagnostic tool for identifying the causative allergen 2, 4

Treatment and Prevention

• Treatment involves avoiding the suspected irritants or allergens, restoring the skin barrier, and reducing skin inflammation through multiple treatments 2
• Topical corticosteroids can be used to treat exacerbations, but should be avoided in long-term treatment 4
• Preventive strategies include avoiding exposure to triggering allergens, using barrier creams and moisturizers, and implementing standard of care interim treatments 5

Blanching of a Rash

• There is no direct evidence in the provided studies that specifically addresses the blanching of a rash in the context of contact dermatitis
• However, it is known that contact dermatitis can cause erythema (redness) and other skin changes, but the blanching of a rash is not a characteristic that is typically highlighted in the diagnosis or description of the condition 2, 4, 3, 6, 5