Babies have delicate skin, so they develop rashes more easily than adults. Because their skin is thin and unmarked by hair, old scars, sun spots and other skin conditions acquired with age, rashes also might be more visible on babies. Although most childhood diseases associated with rashes cause an all-over rash, several conditions could cause a rash that appears like a red line on your baby's skin. Call your child's doctor if she has a rash.
Exposure to an allergen can cause a red rash in a line on a baby. A baby allergic to elastic, for example, might develop a contact dermatitis rash only around his waist or around his legs, where the elastic touched his skin. Removing the offending allergen usually clears up a localized allergic reaction. Call your doctor if your baby has a systemic allergic reaction such as facial swelling, difficulty breathing or vomiting and diarrhea. Let your doctor know if the rash spreads to other areas or if hives, pinkish welts that move from one area of the body to the other, appear.
Insect bites can also appear as a red line that resembles a rash. Bedbugs might bite in a straight line. Bedbug bites can cause intense itching. Getting rid of the bedbugs takes an exterminator and dogged effort. Scabies can also cause a red line rash when parasites tunnel under the skin, causing localized irritation. Scabies often develops on the hands, fingers, outside of the elbows, lower abdomen or genitals, but can also occur on the face, scalp, palms or soles of the feet in babies. Scabies treatment consists of covering the entire body with a prescribed ointment. Scabies can take two to six weeks to resolve, according to BabyCenter.
If your baby has a red streaky rash that runs along a vein, she might have cellulitis, a skin infection, especially if she has a break in the skin nearby. A red line on the face can occur in erysipelas, another skin infection that often occurs near a break in the skin. Group A streptococcus most commonly causes both infections. Your baby might run a fever and act lethargic and unwell. Both these conditions require medical treatment and antibiotics. Impetigo, another bacterial infection, can also cause a red line rash. Antibiotic ointments or oral antibiotics are used to treat impetigo.
If your baby wears tight clothing in the summer, he might develop a fine prickly heat rash across his forehead under the tightest part of his hat or near the waistband of his pants. Prickly heat, which occurs when sweat glands become blocked, will resolve when you cool down the area. Heat rashes can cause itching; cool baths and applying lotions that cool down the skin can help.