Cellulitis and Skin Infections: What Needs an Antibiotic, What Needs Draining, and What Is Not Infected

A red, hot, swollen area of skin gets one of three completely different answers: tablets, a scalpel, or nothing at all. Getting that wrong is common in both directions — people take antibiotics for skin that is not infected, and people take antibiotics for pus that needed opening.

🗺️ The map: same redness, different depth

Skin infections are separated by how deep they sit, and the depth decides the treatment far more than the name does.

🦿 What cellulitis actually looks like

• 🔹 One side only. Almost always a lower leg, sometimes an arm or the face
• 🔹 Warm to the touch, tender, and spreading over hours to a day or two
• 🔹 The border is vague, fading into normal skin rather than stopping at a line
• 🔹 There is usually an entry point, and it is often tiny — a crack between the toes, a scratch, an insect bite, an ulcer, a shaving nick, a patch of eczema
• 🔹 Fever occurs in a minority, so being afebrile does not argue against it
• 🔹 Red streaks running up towards the groin or armpit, with a tender swollen node there, mean the lymphatics are involved. It looks alarming and it responds to the same treatment
• 🔹 Blisters on the surface can occur in more severe cellulitis and are not automatically a sign of necrotising infection, though they raise the threshold for a proper look

🚨 The pattern that goes to surgery, not to a pharmacy

🧐 The red leg that is not infected

This is where most unnecessary antibiotics go. If redness has been present for weeks, is on both legs, itches rather than hurts, or has a border matching the shape of something that touched it, think again.

🔪 Boils and abscesses: why tablets are the side dish

The principle here is the same one that governs a dental abscess, and it is worth stating plainly: an antibiotic carried in the blood cannot reach the middle of a pocket of pus, because that space has no circulation. Explained at length in what antibiotics can and cannot do for a tooth infection.

• 🌡️ A warm compress several times a day helps a developing boil come to a head and often lets it drain on its own
• ✂️ Incision and drainage is the definitive treatment for a fluctuant abscess. Relief is usually immediate, because the pain was pressure
• 💊 Antibiotics are added when there is surrounding cellulitis, when it is large or on the face, when the person is systemically unwell, immunosuppressed or diabetic, or when drainage was incomplete
• 🚫 Never squeeze a boil on the central face — the area from the bridge of the nose to the corners of the mouth drains towards veins inside the skull. Squeezing there is the one place this advice is more than cosmetic
• 🔄 Boils that keep returning usually mean Staphylococcus aureus living in the nose. A short course of Bactroban (Mupirocin) in the nostrils plus an antiseptic wash is how that cycle is broken, and it is far more effective than another course of tablets
• 🧴 Keep towels, razors and flannels personal while boils are active, since it spreads within households easily
• ⚠️ Recurrent boils in the armpits or groin with scarring and tunnels are probably not boils at all but hidradenitis suppurativa, which is treated completely differently

💊 Which antibiotic, and why not the others

⏱️ How long, and what getting better looks like

Expectations here are wrong in a specific and predictable way, and it leads to unnecessary changes of antibiotic.

• 📅 Five to six days is enough for most uncomplicated cellulitis. The old ten to fourteen day habit has gone, and longer courses do not lower recurrence
• ⚠️ The redness often expands for the first 24 to 48 hours while the treatment is working. What should improve first is fever, pain and how unwell the person feels. Judging success by the red area in the first two days leads to switching a drug that was fine
• 🖊️ Draw round the edge with a pen and write the time. It turns a vague impression into a measurement, and it is the easiest thing anyone can do at home
• 🦵 Elevate the leg above the level of the hip whenever sitting. This is the single most underused measure in leg cellulitis and it does more for the swelling than any tablet. Walking around all day with the leg down slows recovery considerably
• 🟤 The colour fades last, over two to four weeks, and a brownish stain can persist for months. That is healing, not continuing infection
• 🚩 No improvement in fever and pain by 48 to 72 hours means a rethink: an undrained abscess, a resistant organism, a deeper infection, or the diagnosis being wrong in the first place
• 🍄 Antibiotics have costs — diarrhoea, thrush and resistance. New watery diarrhoea during or after a course needs attention rather than an anti-diarrhoeal; thrush afterwards is common and treatable, as in vaginal candidiasis and the fluconazole dose

🔁 Why it comes back, and how to stop that

Around one in three people who have had cellulitis of the leg has another episode within three years, and each attack damages lymphatic drainage a little more, which makes the next one easier. Prevention is therefore not optional extra advice.

1. 🦶 Treat the toe webs and the toenails. The commonest doorway, and the commonest thing left untreated
2. 🧴 Moisturise daily and treat eczema properly. Dry cracked skin is an entry point, and an itch-scratch cycle keeps opening it — see breaking the itch-scratch cycle
3. 🧦 Compression for leg swelling, once the acute episode has settled. Reducing the oedema reduces recurrence substantially, and it is the measure most often skipped
4. 🩹 Care for any ulcer or wound rather than leaving it open and uncovered
5. 🧪 Control diabetes. High glucose impairs the immune response and slows healing — see choosing the first drug in type 2 diabetes
6. ⚖️ Weight and venous disease both feed the swelling that feeds the infection
7. 💊 Long-term preventive penicillin is offered after repeated attacks. It works while it is taken and the benefit fades after stopping, so it is a decision about years rather than weeks

🐾 Bites, which follow different rules

• 🐱 Cat bites are the worst of the common ones. Needle-thin teeth drive bacteria deep and the surface seals over it, so a tiny puncture on a hand becomes a deep infection. A large share become infected
• 🐶 Dog bites crush more and infect less, though a deep one still needs looking at
• 👊 A cut over the knuckles from hitting a mouth is the highest-risk bite there is. The joint opens when the fist clenches and seals when it relaxes, trapping bacteria inside the joint. It always needs assessment, however small it looks
• 🚫 Bite wounds are generally not stitched closed, because sealing bacteria inside is the problem. Facial wounds are handled differently by a specialist
• 💉 Tetanus cover is checked every time, and rabies risk is assessed for any animal bite depending on the animal and the region
• 🚰 Irrigate immediately and generously with running water. What happens in the first minutes matters more than what is prescribed afterwards
• 🧫 Hands, feet, joints and faces are all higher risk than the same bite on a thigh

🦶 The diabetic foot is a separate problem

🍄 When it is fungal and the cream makes it worse

Fungal infection imitates bacterial infection often enough to matter, and the two are treated in opposite directions.

• 🔹 Ringworm on the body — an expanding ring with a scaly active edge and clearer centre, itchy rather than painful
• 🔹 Between the toes — split, white, soggy skin, which is both an infection and the doorway discussed above
• 🔹 In skin folds — under the breasts, in the groin, under an abdominal fold. Red, moist, often with small satellite spots just beyond the main patch, which is the clue to yeast
• ⚠️ A steroid cream on a fungal rash makes it spread while making it look better for a few days. The itch settles, the fungus grows, and the pattern becomes unrecognisable. If a rash improves on steroid and then returns worse and wider, suspect this
• 💊 Treatment is antifungal — topical for small areas, and oral such as Lamisil (Terbinafine) or Diflucan (Fluconazole) for nails, scalp or extensive skin, chosen by site and organism
• ⏳ Courses are long. Skin takes weeks, toenails take months, and stopping early is the usual reason it returns

🧴 What to put on a wound, and what not to

• ✅ Clean running water and mild soap. That is the evidence-based answer and it beats everything in the cupboard
• ❌ Not hydrogen peroxide, not neat alcohol, not iodine poured into open tissue. They damage the cells doing the healing and do not reduce infection in a simple wound
• 💧 Cover it and keep it slightly moist. Wounds heal faster covered than scabbed dry in the open air, which is the opposite of the usual instinct
• 🧷 Change the dressing when it is wet or dirty, not on a fixed schedule for its own sake
• 🔎 Normal healing means redness confined to a few millimetres at the edge, decreasing day by day, with clear or slightly yellow fluid early on
• 🚩 Infection means redness spreading outwards, increasing pain after day two or three, thick pus, a bad smell, or fever
• 💊 Antibiotic ointment is for an infected wound, not for every graze. Routine use is how resistance to topical antibiotics developed

👶 Children, and the two that need urgency

• 🔹 Impetigo is the commonest — golden crusts around the nose and mouth, highly contagious, treated topically. Children can return to school once lesions are crusted or dry, or after 48 hours of treatment
• 🔹 Redness and swelling around an eye is an emergency, because infection behind the eye socket threatens vision. Pain on moving the eye, a bulging eye or double vision means hospital the same hour
• 🔹 Chickenpox with a rapidly worsening painful area is the classic setting for necrotising infection in a child. Anti-inflammatory medicines are avoided during chickenpox for this reason
• 🔹 Widespread blistering and peeling in a baby or toddler with fever needs assessment the same day
• 🔹 Folliculitis after a hot tub is common, usually resolves without antibiotics, and is caused by a different organism from ordinary folliculitis
• 🔹 Not every pustule is infection. Acne is inflammation of the follicle rather than a treatable infection — see how retinoids and isotretinoin clear acne

📞 When to seek help, and how fast

Same day:

• Redness spreading on a leg, arm or face, especially with fever
• Any infection in a diabetic foot, however small and however painless
• A cat bite, a human bite, or any bite on a hand, foot, joint or face
• A fluctuant lump that needs draining
• No improvement in fever and pain after 48 to 72 hours of antibiotics
• Infection with a weakened immune system — chemotherapy, long-term steroids, transplant medication

Arrange a review if:

• You have had cellulitis twice or more — the prevention plan matters more than the next course of antibiotics
• Both legs are red and you have been given antibiotics for cellulitis
• Redness has been present unchanged for weeks
• Boils keep returning, which usually means nasal carriage rather than bad luck
• A rash improves on steroid cream and then comes back worse and wider
• Your legs swell and you have had one episode of cellulitis

❓ Frequently asked questions

📑 Sources and editorial

• Infectious disease society guidance on the diagnosis and management of skin and soft tissue infections, including the classification by depth, indications for incision and drainage, and antibiotic selection by presentation
• Clinical guidance on cellulitis and erysipelas, including the absence of a confirmatory diagnostic test, the typically unilateral presentation, and treatment duration of five to six days in uncomplicated disease
• Studies of diagnostic accuracy in cellulitis, including the proportion of patients admitted with a cellulitis diagnosis who were found to have an alternative condition, and the conditions most commonly responsible
• Literature on pseudocellulitis, including stasis dermatitis, lipodermatosclerosis, contact dermatitis, gout, deep vein thrombosis, lymphoedema and ruptured calf muscle as mimics
• Guidance on necrotising soft tissue infection, including pain disproportionate to examination findings as the earliest sign, the associated systemic features, risk groups, and the requirement for urgent surgical debridement rather than antimicrobial therapy alone
• Guidance on the management of cutaneous abscess, including the primacy of drainage and the defined circumstances in which adjunctive antibiotics add benefit
• Evidence on tinea pedis and interdigital maceration as a portal of entry for lower limb cellulitis, and on treatment of the feet as a preventive measure
• Evidence on recurrence rates after an episode of lower limb cellulitis and on the role of oedema reduction, compression therapy and skin care in prevention
• Trial evidence on long-term antibiotic prophylaxis for recurrent cellulitis, including the loss of benefit after discontinuation
• Guidance on Staphylococcus aureus decolonisation with intranasal mupirocin and antiseptic washing for recurrent furunculosis
• Guidance on impetigo, including topical antibiotic therapy for localised disease, oral therapy for extensive disease, and return-to-school criteria
• Prescribing information for cephalexin, clindamycin, trimethoprim with sulfamethoxazole, doxycycline, azithromycin, amoxicillin with clavulanate and topical mupirocin
• Guidance on methicillin-resistant Staphylococcus aureus in skin infection, including risk factors and the absence of MRSA coverage with first-generation cephalosporins
• Guidance on the management of mammalian bite wounds, including the microbiology of cat, dog and human bites, the avoidance of primary closure, clenched-fist injuries over the metacarpophalangeal joints, and tetanus and rabies assessment
• Guidance on diabetic foot infection, including probe-to-bone assessment for osteomyelitis, the effect of neuropathy on pain as a guide, vascular assessment, and daily foot inspection
• Guidance on fluoroquinolone safety restrictions and their limited activity against streptococci in skin infection
• Literature on contact sensitisation to topical neomycin and on rising fusidic acid resistance associated with widespread topical use
• Guidance on superficial fungal infection of the skin, nails and skin folds, including the effect of topical corticosteroid on presentation and course, and treatment durations by site
• Evidence on wound cleansing, including the absence of benefit and the cytotoxicity of hydrogen peroxide and alcohol in open wounds, and the advantage of moist wound healing
• Guidance on periorbital and orbital cellulitis in children, and on the association between varicella infection, non-steroidal anti-inflammatory use and invasive streptococcal infection
• Related reading: what antibiotics can and cannot do for a tooth infection, thrombosis and embolism warning signs, shingles and the 72-hour window, contact dermatitis, breaking the itch-scratch cycle, leg pain when you walk, acne and how retinoids clear it
• Related products: Keflex (Cephalexin), Bactroban (Mupirocin), Cleocin (Clindamycin), Bactrim, Doxycycline, Augmentin, Lamisil (Terbinafine), antifungal range
• RXshop Editorial Team — reviewed by Emily Chen, MD, MPH — Internal Medicine Specialist