3.3 Immunity and Body Defenses

Immunity and Body Defenses

Exam Focus: This bullet is short in the curriculum but reliably examined. Know the four layers of defence — physical, chemical, cellular, systemic — the acid mantle pH range, the distinction between natural and acquired immunity, and the professional inference: an intact barrier is the reason a healthy client tolerates services that would infect broken skin.

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1. Four Layers of Defence

The human body resists infection at four levels. A cosmetologist works at the outermost of them all day long.

2. Unbroken Skin: The Cosmetologist's Working Assumption

Almost every safety rule in Part 160 makes sense once you see that it protects a barrier.

• The rule that no chemical service is performed over abraded, inflamed or broken scalp skin exists because the barrier is gone. Alkaline relaxer or lightener on intact scalp is uncomfortable; on broken scalp it is a chemical burn with an open portal of entry.
• The rule that a client should not shampoo vigorously before a relaxer service exists for the same reason — scratching creates micro-abrasions.
• § 160.20(i) requires gloves for any procedure that risks breaking the client's skin, because that is the moment the barrier fails.
• § 160.18(a)(2) bans reusing a razor, and § 160.18(a)(5) bans credo knives, because both cut living tissue.
• § 160.19 treats all blood as infectious, because blood only appears once a barrier has already been breached.

3. The Acid Mantle

The acid mantle is the thin film of sebum, perspiration and lipids on the skin and hair surface, naturally maintained at pH 4.5 to 5.5. It matters in three ways:

1. It inhibits microbial growth. Most pathogenic bacteria and fungi grow poorly in a mildly acidic environment.
2. It keeps the cuticle compact. Acidic products contract and harden the hair cuticle; alkaline products swell and lift it. That is the whole basis of chemical service chemistry, covered in Chapter 5.
3. It is temporarily disrupted by professional services. Permanent waving solution at pH 9.0–9.6, hydroxide relaxer at pH 11.5–14, and oxidative colour at pH 9–10 all raise skin and hair pH sharply.

The professional response is built into service protocols: acid-balanced normalising or neutralising shampoos after chemical services, acidic conditioning rinses to re-close the cuticle, and protective base cream on the scalp and hairline before hydroxide relaxers.

4. Natural and Acquired Immunity

The hepatitis B vaccination is the acquired-immunity example most relevant to this trade. OSHA's Bloodborne Pathogens Standard requires employers with occupational exposure to make the vaccine available to at-risk employees at no cost. Salon practitioners handle sharp implements around skin daily, and HBV is far more transmissible than HIV through a small percutaneous exposure.

5. Immunity Is Not a Substitute for Procedure

Two errors follow from misunderstanding immunity, and both appear on exams.

• "I'm healthy, so I don't need gloves." Innate immunity does not protect against a percutaneous exposure to a bloodborne virus. § 160.19 requires disposable gloves whenever contact with blood can reasonably be anticipated, regardless of the practitioner's health.
• "The client looks fine, so the implement is fine." Many clients carrying a bloodborne virus are asymptomatic and unaware. That is the entire logic of universal precautions: every client is treated as though their blood is infectious, so behaviour does not depend on appearance or disclosure.

The compensating professional habits are unglamorous and effective: wash hands with soap and water before every service, keep your own skin intact and cover your own cuts with a waterproof dressing before working, use gloves for chemical and risk-of-bleeding procedures, and reprocess implements to the New York standard between every client.