What should you know about rash after spider bite?

A small area of redness, swelling, warmth, or itch can occur around an insect bite and may settle as the skin reacts. Many bites are not witnessed, so a spreading rash is not proof that a spider caused it. A contact reaction, follicle irritation, bacterial infection, or another condition can look similar. Note whether the area is expanding, whether pain is greater than itch, and whether a blister, dusky centre, drainage, or red streak appears. Itching elsewhere or in household contacts can point toward a different cause such as Scabies rather than one isolated bite.

Gently wash the area, use a cool compress, and avoid squeezing, cutting, or applying household chemicals. Keep nails short and do not scratch a blister. Marking the edge of redness with a pen and taking a dated photograph can help show whether it is spreading. A pharmacist or clinician can advise about an appropriate itch treatment after considering your age, medicines, and health conditions. Do not use leftover antibiotics or steroid creams on an unexplained lesion without advice. Arrange review if the rash is not settling or if you are unsure what caused it; Contact Dermatitis and Drug Rash can mimic bite reactions.

Get urgent help for breathing difficulty, facial or throat swelling, dizziness, faintness, or widespread hives. Seek same-day medical care for rapidly enlarging redness, severe or increasing pain, skin breakdown, a darkening centre, pus, red streaks, fever, vomiting, muscle cramps, or feeling very unwell. A bite near the eye, mouth, or genitals also deserves prompt advice. Children, older adults, and people with reduced immunity should be assessed early when redness is spreading or the skin is painful.

Does this look like a bite reaction or infection? Should the area be measured or photographed? What symptoms would mean I need urgent reassessment, and which treatments are safe with my current medicines?