Why does inflammation cause redness?

What happens beneath the skin?

Inflammation is your immune system's natural response to injury or infection and helps the body deal with invading germs. Skin itself forms part of the immune system's first line of defence, rather more work than serving as a display shelf for skincare.23

When tissue is injured by bacteria, trauma, toxins or heat, damaged cells release chemical signals. These include histamine, bradykinin and prostaglandins, which is an elaborate cast list for explaining a colour. Histamine causes blood vessels to expand, a process called vasodilation. Increased blood flow in inflamed skin produces the visible redness.134

The chemical signals also make blood vessels leak fluid into nearby tissue, causing swelling. This helps isolate foreign substances from surrounding tissue. The signals attract white blood cells called phagocytes, which remove germs and dead or damaged cells. Redness and swelling therefore have related but different causes: redness comes from increased skin blood flow, while swelling comes from fluid entering the tissue.3

Is redness a sign of inflammation?

Yes, redness can be a sign of inflammation, but the two are not interchangeable. Inflammation can occur without redness, and redness can occur without inflammation. Look at changes in warmth, tenderness, swelling and texture as well as colour. Erythema is the medical word for redness.1

A red eye illustrates why colour alone cannot identify the cause. Surface blood vessels can become swollen or dilated, making the eye look bloodshot. A separate bright red spot can result from a broken vessel after coughing or straining, often without pain or a change in vision.5

Does inflammation look red on every skin tone?

Redness is easiest to see in lightly pigmented skin. In darker skin, inflammation can appear purple, grey, brown, dark brown or black, as well as red. Colour changes can be subtle, so also look for tenderness, warmth, swelling, peeling, raised bumps or changes in the skin's surface. Less visible redness does not mean less inflammation.1

Inflammation can also affect pigment production. Melanin is the pigment that determines skin colour, and inflammatory signals can increase its production. The resulting darkening is called postinflammatory hyperpigmentation. A darkened patch and visible redness are therefore different colour changes associated with inflammation, not two names for the same thing.6

Does blocking histamine treat every kind of redness?

Antihistamines block histamine's effects and are commonly used for allergy symptoms, including hives and reactions to insect bites or stings. Allergies happen when the immune system responds to something usually harmless. Antihistamines are an option for allergy symptoms, not a treatment to choose simply because skin looks red. Follow the exact medicine's leaflet or a pharmacist's directions. Ask a pharmacist or doctor before taking one if you are pregnant, breastfeeding, taking other medicines or have an underlying health condition.4

When does redness need medical attention?

Facial redness with breakouts can occur in both acne and rosacea, which need different care. A dermatologist can identify which condition is present. Deep acne breakouts, such as cysts, require prescription treatment, while appropriate rosacea care can help prevent worsening.7

For eye redness, pain or vision problems matter more than colour alone. Contact an eye doctor immediately if eye pain comes with a vision problem. Seek medical advice if redness lasts longer than one to two days.5