Why it matters: you can't stop what you can't name. The written exam asks you to identify germ types, shapes and the conditions they cause, and in the shop you need to spot when a client shouldn't be in your chair today.

Germs (microorganisms) come in four groups that matter to barbers.

Bacteria are one-celled organisms found almost everywhere. Most are nonpathogenic, meaning harmless or even helpful. Pathogenic bacteria cause disease. Know them by shape:

Type	Shape	Examples
Cocci	Round	Staphylococci grow in clusters like grapes (boils, skin infections). Streptococci grow in chains (strep throat)
Bacilli	Rod-shaped	The most common type: tetanus, tuberculosis
Spirilla	Spiral or corkscrew	Syphilis, Lyme disease

MRSA is a staph bacteria that resists many antibiotics. It spreads through skin contact and shared items like towels, capes and tools. A small red bump that looks like a pimple or spider bite can be MRSA.

Viruses are much smaller than bacteria and can only reproduce inside living cells. They cause colds, flu and fever blisters (herpes simplex). Antibiotics don't kill viruses.

Bloodborne pathogens travel in blood and body fluids. The three to know: hepatitis B (HBV), hepatitis C (HCV) and HIV. Hepatitis B can survive on a surface outside the body for days, which is why a tiny nick on a clipper blade matters.

Fungi include molds and the fungi that cause tinea (ringworm). Ringworm is a fungus, not a worm. Tinea capitis is ringworm of the scalp: round, scaly patches, sometimes with broken hairs. Tinea barbae, or barber's itch, is ringworm of the beard area.

Parasites live on or in another living thing. Pediculosis capitis is head lice. Scabies is tiny mites that burrow under the skin and cause intense itching.

Do it: what to do when you see something

Look at the scalp and skin during your consultation, before you start.
If you see signs of lice, scabies, ringworm, an open or infected sore, or a rash you can't identify, don't start the service.
Tell the client privately and kindly. You're not diagnosing; you're protecting them and the next client.
Suggest they see a doctor and come back when it's cleared.
Clean and disinfect anything that touched them, and wash your hands.

V's rule: lice, scabies, ringworm or an infected sore means no service today. Decline kindly, privately, and suggest they see a doctor.

Common mistakes

Mixing up shapes: cocci are round, bacilli are rods, spirilla are spirals.
Thinking ringworm is a worm, or that antibiotics treat viruses.
Cutting "around" a problem spot to keep the client happy.

What the state board looks for: shape and grouping questions (staph = clusters, strep = chains), which conditions are fungal, bacterial or parasitic, and that you refuse service for contagious conditions.

Check yourself

Staphylococci grow in what pattern?
What is tinea barbae more commonly called?
A client has head lice. What do you do?

Answers

Clusters.
Barber's itch.
No service today. Tell them privately, suggest a doctor, then clean and disinfect everything they touched.

Go deeper: E-book 3, Infection Control · E-book 7, The Skin: Structure, Disorders & Diseases · E-book 8, Properties & Disorders of the Hair & Scalp.