Flea bites may or may not have a red spot at their centers. This red pinpoint is known as a hemorrhagic punctum, and it’s caused by a ruptured blood vessel.
A red dot, about the size of pinpoint, is sometimes present in the middle of a flea bite. This is where the skin and blood vessel were ruptured by a feeding flea. The puncture mark is called the hemorrhagic punctum.
What Causes the Red Mark
Flea mouth parts are highly adapted for piercing skin. When a flea feeds, it inserts a single needle-like stylet (median epipharynx) into a blood vessel. As a result, there’s only one puncture mark per bite. When the stylet is removed from the host, the hemorrhage is slight or absent. The bites cause surprisingly little damage.
When the Red Mark is Absent
The hemorrhagic punctum will be absent if the flea didn’t successful locate a blood vessel. This is common, as fleas usually probe a few areas before finally feeding. However, each probe site still provokes an allergic reaction.