Unless you saw the spider, it is probably not a spider bite: the CDC notes most suspected spider bites are staph or MRSA skin infections, a red, swollen, painful, warm, pus-filled bump that grows over 24-48 hours.
Real significant spider bites are rare: most spiders cannot pierce skin, black widow bites cause body-wide muscle cramping more than a skin lesion, and brown recluse ulcers are region-specific and take days to develop. The behavioral tell: infection worsens, heats up, and may add fever or red streaks; a simple bite stays stable and fades. The rules: never squeeze or pop it (that spreads bacteria), cover it, wash hands, and see a provider, urgently if worsening fast, not improving in 48 hours, or feverish, because MRSA often needs drainage plus specific antibiotics. While it heals: no shared towels, razors, or gym gear, and wash bedding, since MRSA spreads person to person. The ER version: spreading infection with fever, confusion, or racing heart, or a bite followed by severe cramping or breathing trouble.
What to do
Common questions
Spider bite vs MRSA: how to tell?
The CDC says it directly: people constantly mistake MRSA skin infections for spider bites, and unless you actually saw the spider bite you, the bump is far more likely to be a bacterial skin infection. The MRSA or staph look: a red, swollen, painful, warm bump, often with pus or drainage, sometimes described as a pimple or boil that keeps growing, possibly with a honey-colored crust, and it can turn into a deep abscess. The spider-bite reality: most spiders cannot even pierce human skin; true significant bites are rare, usually a small red bump that fades, and the famous dangerous ones are region-specific (black widow: muscle cramps and whole-body symptoms more than a skin lesion; brown recluse: a blister that can break down into an ulcer over days, mostly in the south-central US). The behavioral difference that matters: an infection grows, gets hotter and more painful over 24 to 48 hours, and may bring fever or red streaks running from it; a simple bite stays stable and fades. The action rules, per the CDC: do not squeeze or pop it (that spreads the infection), cover it with a clean dry bandage, wash hands after touching it, and see a healthcare provider, urgently if it is rapidly worsening, not improving within 48 hours, or comes with fever, because MRSA needs drainage and sometimes specific antibiotics that plain keflex will not cover. MRSA spreads person to person and through shared items: keep the area covered, do not share towels, razors, or gym equipment, and wash bedding. The genuinely emergent version: a spreading infection with fever, confusion, or rapid heart rate, which can be sepsis, or a bite with severe muscle cramping or difficulty breathing, the black widow pattern: ER.