Flea bites are almost always red, regardless of the lesion type. Pink inflammation may surround the bite. Occasionally, affected skin slightly darkens (hyperpigmentation). Skin sometimes dies at the bite’s center, turning dark red. If a bite becomes infected, it may contain white pus.
Flea bites appear within 15 minutes. Skin elevates (wheals) at the bite location. Reddening, called erythema, often surrounds the wheal as blood capillaries dilate. Wheals have an irregular shape and size. Sometimes they aren’t clearly defined, while other times they’re outlined by a red halo.
Delayed reactions appear 24 hours after the bite, usually in the form of papules (welts). Skin around papules may or may not turn red. A bright pink circle sometimes surrounds the lesions. The papules may develop necrotic (dead skin) centers, appearing dark red or black. Occasionally, delayed reactions appear as hyperpigmentation (slightly darkened skin).
Blister-like eruptions, called bullae, are extreme reactions to flea bites. The fluid-filled lesions may appear red or translucent, with accompanying erythema at their base. The blistered skin often dies and darkens (epidermal necrosis).
In rare circumstances, extravasated flaring can occur around a flea bite. Skin in the area becomes inflamed and turns a splotchy, dark red. This is caused by white blood cells moving from capillaries to the tissue surrounding the bite.
Some individuals react to flea bites with hemorrhagic macules. These are rashes which appear as small, red, splotchy areas of discolored skin.
Scratching flea bites can temporarily relieve itching. However, it also causes inflammation, making the bites itch even more. This is known as the scratch-itch cycle. Scratch marks and inflamed skin will look bright red or pink.
A red puncture mark, called the hemorrhagic punctum, can be present at the center of flea bites. It’s about the size of a pinpoint and results from the blood vessel rupturing. Sometimes it’s absent, especially if the flea couldn’t locate a blood vessel.
Flea bites often provoke scratching. And scratching can trigger secondary bacterial infections. Infected bites often become pustules or boils. These lesions resemble pimples, as they’re red with white, pus-filled tips.
Flea bites typically fade away within a few days. A pale, red stain is all that remains, but it too disappears within a couple weeks. However, scratching or rubbing the bites will prolong the healing time. Like pimples, secondary infections leave skin discolored for an extended period of time.