2.1 Microbiology, the Chain of Infection & Levels of Infection Control
Key Takeaways
- Cleaning with soap and water always comes before disinfection or sterilization — it removes debris that would otherwise shield pathogens from the chemical process.
- New York requires implements that touch skin to be immersed in an EPA-registered hospital-grade disinfectant for no less than 10 minutes (19 NYCRR § 160.17).
- Sterilization destroys all microbial life, including bacterial spores, and applies only to implements that penetrate the skin — not routine tools used on intact skin.
- The chain of infection has six links — pathogen, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host — and breaking any one link stops transmission.
- Bacteria are classified by shape: cocci (round, e.g., staphylococci and streptococci), bacilli (rod-shaped), and spirilla (spiral-shaped).
2.1 Microbiology, the Chain of Infection & Levels of Infection Control
Infection control is one of the most heavily tested safety topics on the New York esthetics written exam, and it starts with understanding what you're protecting clients from. Every disinfection protocol you'll ever perform exists to interrupt the life cycle of microorganisms before they can cause disease. This section covers the microorganisms relevant to a spa or esthetics setting, the six-link chain that lets an infection spread from one person to another, and the three distinct levels of decontamination — cleaning, disinfection, and sterilization — that New York requires estheticians to understand and apply correctly.
Microorganisms an Esthetician Should Recognize
Bacteria
Bacteria are single-celled microorganisms present almost everywhere, including on skin, in the air, and on salon surfaces. Most bacteria an esthetician encounters are non-pathogenic — harmless or even beneficial organisms that make up the skin's normal flora. Pathogenic bacteria, by contrast, are disease-causing and are the reason infection-control procedures exist at all. Bacteria are classified by shape, and recognizing the three shapes helps you understand how a bacterial infection presents:
- Cocci — round, dot-shaped bacteria. They often occur in patterns: staphylococci form grape-like clusters and are linked to abscesses, pustules, and boils; streptococci form chains and are linked to infections such as strep throat and some skin infections; diplococci form pairs.
- Bacilli — rod-shaped bacteria. Illnesses associated with rod-shaped organisms include tetanus and tuberculosis.
- Spirilla — spiral or corkscrew-shaped bacteria. Syphilis is caused by a spiral-shaped organism.
Viruses
Viruses are far smaller than bacteria and cannot reproduce on their own — they must invade a living host cell and hijack its machinery to multiply. Because they live inside cells rather than on inert surfaces, viruses can be harder to destroy with the same methods used against bacteria. Two viruses matter directly to esthetics practice: herpes simplex (cold sores/fever blisters) and human papillomavirus (HPV), which causes verrucae (warts). Both are considered contraindications for many services and require the esthetician to recognize the lesion and decline or modify treatment.
Fungi
Fungi include molds and yeasts. Tinea (commonly called ringworm, despite not being caused by a worm) is a fungal skin infection that thrives in warm, moist environments — exactly the conditions found in a spa. Fungal infections are contagious through direct and indirect contact, which is another reason implements must be properly decontaminated between clients.
Parasites
Parasites live on or inside a host and depend on that host for survival, often causing direct harm. Head lice and scabies mites are the parasites most relevant to a spa setting — both cause highly contagious skin or scalp conditions. An esthetician who identifies signs of a parasitic infestation must decline service and refer the client to a physician rather than attempt to treat or work around the condition.
The Chain of Infection
The chain of infection describes the six conditions that must all be present, in sequence, for an infectious disease to spread from one person to another. Because every link is required, breaking any single link stops transmission — this is the entire logic behind hand hygiene, disinfection, and PPE.
| Link | Definition | Esthetics Example | How the Chain Is Broken |
|---|---|---|---|
| Pathogen | The disease-causing organism itself | Bacteria on an unwashed extractor | Proper cleaning and disinfection destroys the pathogen |
| Reservoir | Where the pathogen lives and grows | An infected client, a pooled water basin, a soiled towel | Refusing service to visibly infected clients; not reusing soiled linens |
| Portal of Exit | How the pathogen leaves the reservoir | Broken skin, blood, respiratory droplets | Covering coughs/sneezes; gloving when handling blood |
| Mode of Transmission | How the pathogen travels to a new host | A shared, undisinfected tool touching two clients | Disinfecting every implement between clients |
| Portal of Entry | How the pathogen enters a new host | Broken skin, mucous membranes, eyes | Wearing gloves and eye protection; not working over open lesions |
| Susceptible Host | A person capable of becoming infected | Any client with lowered immunity or broken skin | General sanitation reduces the pathogen load a host is exposed to |
An esthetician cannot control every link, but disinfection and hand hygiene are the links you control directly in every single service — which is exactly why they are tested so heavily.
The Three Levels of Decontamination in the Treatment Room
New York recognizes three distinct levels of decontamination, and they are not interchangeable — each has a specific purpose, and skipping a step undermines the ones that follow.
| Level | What It Does | Method | When It's Used |
|---|---|---|---|
| 1. Cleaning | Physically removes visible debris, oils, and organic matter | Soap/detergent and water, scrubbing, rinsing, drying | Always the required first step, before any disinfectant or sterilant is applied |
| 2. Disinfection | Destroys most pathogenic organisms on non-porous, non-living surfaces and implements | EPA-registered hospital-grade disinfectant, applied per label instructions | Standard requirement for reusable esthetics tools that touch skin (rollers, extractors, tweezers, etc.) |
| 3. Sterilization | Destroys all microbial life, including bacterial spores — the highest level of decontamination | Autoclave (steam under pressure) or extended immersion in an EPA-registered liquid sterilant | Required only for implements that penetrate the skin or draw blood; not required for routine, non-invasive esthetics tools used only on intact skin |
Cleaning always comes first. Disinfectants and sterilants are formulated to kill microorganisms on a physically clean surface — oil, makeup residue, or wax buildup left on a tool can shield pathogens from the chemical and make the disinfection step ineffective, even if the tool sits in the solution for the full contact time. This is why every New York decontamination protocol you'll be tested on begins with soap-and-water cleaning, never straight to disinfectant.
Why must an esthetician clean an implement with soap and water before placing it in disinfectant solution?
A client shows a lesion consistent with tinea (ringworm) on her forearm. What category of microorganism causes this condition?
An esthetician disinfects a metal comedone extractor after use instead of letting the next client use it straight from the drawer. Which link of the chain of infection is this action targeting?
Which statement correctly distinguishes sterilization from disinfection in a New York esthetics practice?