MMRSA Guide
Microscopic illustration of MRSA (Staphylococcus aureus) bacteria
Reference · Staph infection

Staph infection

Staphylococcus aureus lives harmlessly on about a third of us. When it gets through the skin it causes boils, abscesses, infected wounds and cellulitis. MRSA is the antibiotic-resistant version of the same bacterium — this page covers both, and points to the detail on each.

Written by David Roberts, editor · Updated

Checked against current CDC and IDSA guidance. Not medically reviewed. How we source this

Staph, MSSA and MRSA

"Staph infection" nearly always means Staphylococcus aureus. Laboratories then split it into two groups by antibiotic susceptibility: MSSA, which responds to the ordinary penicillin-family drugs, and MRSA, which does not. The bacterium is the same shape, spreads the same way and causes the same infections; only the treatment changes. See MSSA vs MRSA for the full comparison.

What a staph infection looks like

On the skin, staph produces a small set of recognisable patterns. Almost everyone searching for pictures is looking at one of these:

  • Boil or abscess — a deep, painful, pus-filled lump. Full detail
  • Folliculitis — small pus-topped bumps around hair follicles. Full detail
  • Cellulitis — a flat, spreading, hot red area rather than a lump. Full detail
  • Infected wound — a cut or surgical site that turns red, weeps and stops healing.
  • Something taken for a spider bite — the most common first impression. Staph vs pimple

For a full visual walkthrough, see what MRSA and staph lesions look like.

Is a staph infection contagious?

Yes, by contact rather than through the air. It travels on hands, on skin-to-skin contact and on shared objects — towels, razors, bedding, gym equipment, dressings. Intact skin is a good barrier, so the risk is concentrated where skin is broken. A draining lesion is treated as contagious until it is covered, dry and healing.

The setting-by-setting detail lives on is MRSA contagious? — the same rules apply to ordinary staph.

How staph infections are treated

The single most important step for an abscess is drainage; antibiotics alone often will not clear a walled-off collection of pus. Which antibiotic follows depends on the culture result:

SituationUsual approach
Small abscess, otherwise wellIncision and drainage; antibiotics sometimes not needed
MSSA skin infectionFlucloxacillin, dicloxacillin or cephalexin
MRSA skin infectionDoxycycline, trimethoprim-sulfamethoxazole or clindamycin
Bloodstream or deep infectionIntravenous therapy in hospital, typically two weeks or more

The full drug-by-drug picture is on every MRSA antibiotic, and the practical treatment path is on treating skin and soft-tissue infection.

When to seek help urgently

  • Fever or chills alongside a skin lesion
  • Redness spreading quickly, or red streaks running from the wound
  • Severe pain, or a lesion growing by the hour
  • Any significant lesion in a baby, or in someone with diabetes, cancer treatment or a weakened immune system
  • Confusion, breathlessness or feeling profoundly unwell — see when staph and MRSA become dangerous

Preventing another one

Wash hands, keep wounds covered until healed, do not share towels or razors, wash bedding and towels hot, and clean shared gym equipment before use. If infections keep returning in the same person or household, ask a clinician about decolonisation and read why MRSA keeps coming back.

Frequently asked questions

What is a staph infection?
An infection caused by Staphylococcus aureus, a bacterium that lives harmlessly on the skin and in the nose of roughly one in three people. It becomes an infection when it gets through the skin barrier — into a cut, a graze, a hair follicle, a surgical wound or around a medical device.
What does a staph infection look like?
Most often a red, swollen, warm and painful lump that may fill with pus — a boil, abscess or infected hair follicle. It can also appear as honey-crusted sores (impetigo), a spreading flat red area (cellulitis), or a wound that turns red, weeps and stops healing. Many people first mistake it for a spider bite.
Is a staph infection contagious?
Yes, by contact. Staph spreads through skin-to-skin touch and through shared objects such as towels, razors, bedding and sports equipment. It does not usually spread through the air. An open or draining lesion is the most contagious; carriers with no symptoms can also pass it on.
How do you get a staph infection?
Usually from your own bacteria entering broken skin — a shaving nick, a scratch, eczema, an insect bite or a surgical incision — or from contact with someone else's infected skin or a contaminated shared item. Crowded settings with shared kit, such as gyms, teams, care homes and hospitals, see the most transmission.
What antibiotics treat a staph infection?
It depends on whether the strain is MSSA or MRSA. MSSA responds to flucloxacillin, dicloxacillin or cephalexin. MRSA does not respond to those and is treated with doxycycline, trimethoprim-sulfamethoxazole or clindamycin for skin infection, or intravenous vancomycin and similar drugs when the infection is serious. An abscess also needs draining.
What is the difference between staph and MRSA?
MRSA is a type of staph. All MRSA is Staphylococcus aureus; the difference is that MRSA has acquired resistance to methicillin and the whole penicillin-type family, so the usual first-choice antibiotics do not work. A laboratory culture is what tells the two apart.
Can a staph infection go away on its own?
A small boil sometimes drains and heals by itself. Anything larger, spreading, very painful, or accompanied by fever should be seen — untreated staph can move into deeper tissue and the bloodstream. Never squeeze a lesion to try to force it open.
How long does a staph infection last?
An uncomplicated skin infection typically settles over one to two weeks once it has been drained and treated. Deeper infections take longer, and bloodstream infection needs weeks of intravenous treatment in hospital.
References
  1. CDC. Staphylococcus aureus and MRSA infections (2024)
  2. NHS. Staphylococcal infections (2023)
  3. Stevens D.L. et al., IDSA. Practice guidelines for the diagnosis and management of skin and soft tissue infections (2014)
  4. Liu C. et al., IDSA. Clinical practice guidelines for the treatment of MRSA infections (2011)