Flea bites don’t spread. Elevated skin (whealing) forms within 20 minutes of the bite, and it’s replaced by a welt-like papule within 24 hours. By the third day the bite is mostly gone. Scratching a flea bite can worsen the inflammation and the delay healing time. If the skin is broken open, it can result in secondary bacterial infections.
Flea Bites Often Appear in Groups
A single flea will often bite 2-3 times within a few centimeters. So, bites have a tendency to be arranged in a line or triangle. The bite pattern is called a meal cluster or a breakfast, lunch, and dinner configuration.
One Lesion per Bite
To feed, a flea inserts its needle-like stylet into a blood vessel. As a result, there’s one puncture mark per bite. The bite itself cause surprisingly little damage. Each lesion arises from a separate bite.
Before imbibing blood, a flea first finds a good bite location by probing the host’s skin. While probing, anticoagulant saliva is injected into the skin, which helps the flea locate blood. Each probe site causes a bite reaction.
Fleas are easily disturbed while feeding. Slight movements from the person or their clothing can interrupt a flea’s meal. When this happens, the flea will relocate to another feeding site. Subsequent bites will be near the first bite. This causes rows or chains of lesions in close proximity.
Disturbed fleas may temporarily seek refuge in clothing. If it can’t find a way off of the person, the flea may hide in clothing and periodically feed. This may continue for a day or two. However, this is a relatively uncommon situation.
Scratching, Rubbing & Infections
Flea bites are itchy and often induce scratching, especially at night. Scratching can temporarily relieve itching. However, it also causes inflammation, making the bites even more itchy. This is known as the scratch-itch cycle. Even rubbing a flea bite can re-trigger whealing. Flea bites normally fade away within a few days, but scratching or rubbing the lesions will prolong the healing time.
Scratching a bite can break open the skin, cause fluid release, and result in crusting. Secondary bacterial infections aren’t uncommon, and the infection may spread. Infected bites often become pus-filled, pimple-like lesions.
Flea Bite Stages
The first reaction to a flea bite occurs within 20 minutes. An elevated area of skin appears called a wheal. Wheals are irregular-shaped and 2-10 millimeters in diameter. Erythema (reddening) sometimes accompanies the wheal, and can spread beyond 20 mm. The inflammation peaks within a few hours, and is completely gone 12 hours later.
12-24 hours after the bite, the wheal is supplanted by a papule (hard bump). Some people experience a rash covered in tiny bumps (maculopapules). Skin surrounding the lesion may turn red and swell up. A bright pink circle may encompass the area. Papules themselves are 1-3 mm. With surrounding reddening, they can measure up to 20 mm in diameter. The reaction peaks at 24 hours and begins shrinking at 48 hours. They’re often barely recognizable by the third day.
While rare, extravasated flaring can develop around a flea bite. This occurs when white blood cells move from capillaries to the tissue around the bite. As a result, skin in the area becomes inflamed and turns a splotchy, dark red color.
Some people react to flea bites with hemorrhagic macules. These are rashes, appearing as small, red, splotchy areas of discolored skin.
Allergic individuals sometimes experience extreme delayed reactions in the form of blisters. Initially the lesion consists numerous, tiny fluid-sacs called vesicles. The vesicles grow, and in 48-72 hours, they’ll combine into a large blister called a bulla. The reaction peaks 72 hours after the bite. Bullae measure 3-6 mm in diameter.