The Skin Route and What Gloves Actually Stop

Why this matters

Most techs think of skin as a wall and a glove as a second wall. Both leak, in different ways, and the way a glove leaks is the one nobody sees: a solvent can pass straight through an intact, unbroken glove in less time than it takes to clean a part, and keep passing after you have wiped the glove dry. The usual result is not a dramatic injury. It is a tech with red, cracked hands three weeks into a job, wearing a box of the wrong gloves every day and believing they are protected because the gloves never tore.

The skin as a route in

A chemical on skin does one of two things, and they need different thinking.

• Damage at the surface. Corrosives burn, solvents strip the skin's oils, wet work softens the outer layer. The skin is the target.
• Absorption through it. Some chemicals cross intact skin and reach the blood: many solvents, some pesticides, phenols, and a short list of others. The skin is a doorway and the target is somewhere else. Exposure limits flag these with a "Skin" notation in the OSHA tables and NIOSH's recommendations, which means an airborne reading below the limit does not tell you the dose, because part of it arrives through the hands.

Absorption runs faster through skin that is damaged, warm, wet or covered. That last one matters for this card: a glove that lets a solvent in and then holds it against the skin turns a splash that would have evaporated in seconds into an hour of contact under occlusion. A failed glove can be worse than no glove.

See related: Dose, Route, and the Exposure You Cannot See, which owns the dose vocabulary.

Three ways a glove fails

Glove charts and the standards behind them separate three failure modes, and confusing them is how the wrong glove gets picked.

Penetration is bulk flow through a physical opening: a pinhole, a seam, a tear, a split at the thumb crotch. It is the one failure you can sometimes see, and it is what a glove maker's leak test and acceptable-quality-level rating describe. A tear is obvious; a pinhole in a thin disposable is not, which is why a fresh glove is inflated or filled before high-hazard use.

Degradation is the glove material itself changing on contact: swelling, softening, stiffening, cracking, going tacky. It is often visible, and when you see it the glove has already lost its rating. A degradation rating says how well the material holds its physical properties; it says nothing about whether the chemical is getting through.

Permeation is the chemical moving through the intact material at the molecular level: absorbing into the glove's outer surface, diffusing through the thickness, and coming off the inside face. Nothing changes that you can see or feel. A glove can rate excellent on degradation and still permeate a solvent in minutes, which is the single most important sentence on any glove chart.

Breakthrough time and what it does not tell you

Permeation is tested by putting the chemical on one side of a glove sample and measuring when it appears on the other. Two numbers come out.

• Breakthrough time is how long until the chemical is detected on the inside at a defined rate. The US test method is ASTM F739; the European method behind EN ISO 374-1 ratings reports it as performance levels, from level 1 at more than 10 minutes up to level 6 at more than 480 minutes. The two methods use different detection rates, so a figure from one is not directly comparable with the other.
• Permeation rate is how fast it comes through once it has started. Two gloves with the same breakthrough time can differ many times over in what reaches the skin after it.

What the number does not tell you:

• It is measured on continuous contact with the neat chemical at a lab temperature. Splash contact is gentler; hot work, flexing and stretched material are harsher.
• Permeation does not stop when the splash does. Chemical already absorbed into the glove keeps moving inward after you wipe the outside. A disposable glove that was splashed has used part of its breakthrough time, and taking it off, letting it "dry" and putting it back on reuses a glove that is now partly on the wrong side of the chart.
• It is for one chemical. A product is usually a mixture, and the component the glove handles worst sets the result.

Why nitrile is not the answer to everything

Nitrile became the default disposable for good reasons: it handles oils, greases, aliphatic solvents like mineral spirits, alcohols and dilute acids and caustics well, it does not trigger latex allergy, and it tears visibly. That record makes it feel like a chemical glove. Against a few common families it is not.

• Ketones such as acetone and MEK permeate thin nitrile quickly, in some charts in about a minute.
• Chlorinated solvents such as methylene chloride go through nitrile, and through nearly every other common glove material, almost at once.
• Aromatic solvents such as toluene and xylene, common in thinners and adhesive removers, rate fair to poor in nitrile, especially at disposable thickness.

Thickness changes this a great deal. A 4 to 5 mil disposable is a splash barrier for most solvents; a 15 to 22 mil unsupported nitrile gauntlet may last far longer against the same chemical. Never read a rating for one thickness onto another.

The general picture, for typical glove thickness and continuous contact:

GLOVE MATERIAL MATCH - GENERAL GUIDE ONLY
G good  F fair  P poor   (maker's chart governs)

Chemical family        NIT  NEO  BUT  LAT  LAM
Oils, greases           G    G    P    P    G
Aliphatics (spirits)    G    F    P    P    G
Alcohols (IPA)          G    G    G    F    G
Dilute acid/caustic     G    G    G    F    G
Conc. sulfuric acid     P    F    G    P    G
Ketones (acetone)       P    F    G    F    G
Aromatics (toluene)     F    P    P    P    G
Chlorinated solvents    P    P    P    P    G

NIT nitrile  NEO neoprene  BUT butyl
LAT natural rubber latex  LAM laminate film

Butyl handles ketones and is poor against the hydrocarbons; nitrile is the reverse. The laminate film column looks like a winner and is the clumsiest glove you will ever wear, which is why it is usually worn as a liner under a fitted nitrile outer glove that supplies grip and dexterity. Reading the actual chart for the actual product is the job of a sibling card; see related: How to Choose a Glove from the SDS.

The legal floor is that hand protection is chosen for the hazard: 29 CFR 1910.138 requires appropriate hand protection where hands are exposed to skin absorption of harmful substances or chemical burns, selected on the glove's performance against the task, the conditions, the duration and the hazard. Construction work carries the same duty under the general personal protective equipment requirement at 29 CFR 1926.95.

Dermatitis, the disease the glove was supposed to prevent

Contact dermatitis is the most common occupational skin disease, and it comes in two kinds that a clinician distinguishes, not the shop.

• Irritant contact dermatitis, by far the more common, is direct damage: solvents dissolving the skin's oils, wet work, detergents, friction. It builds with repeated exposure and tends to show where contact is heaviest, on the backs of the hands and between the fingers.
• Allergic contact dermatitis is an immune reaction. Once someone is sensitized, small exposures set it off. Epoxy resins, some acrylates, natural rubber latex proteins and some chemicals used in glove manufacture are known causes, which is how a glove can be the trigger.

Gloves themselves contribute: hours of sweat under an occlusive glove soften skin and lower its barrier, so long wear without a break is part of the problem. Cotton liners under a chemical glove, breaks to let skin dry, washing with mild soap rather than solvent, and a plain moisturizer at the end of the day are ordinary controls. A tech whose hands are cracking, weeping or spreading gets seen by a clinician who knows what they work with, rather than switching gloves on a hunch.

Worked example: the spray-gun cleanup that wrecked a painter's hands

A painter on a residential crew cleans a spray gun and its lines with lacquer thinner at the end of each day, about 20 minutes with hands wet the whole time, wearing 4 mil disposable nitrile from the truck box. After three weeks both hands are red and cracked across the knuckles, worse on the right. The gloves have never torn.

The shop reads the thinner's safety data sheet. Its listed components include acetone, toluene and methanol. Against the general table, nitrile is poor on the ketone and fair on the aromatic, and the worst component governs, so the mixture is a poor match before the glove maker's chart is even opened. The maker's chart for that 4 mil glove gives acetone breakthrough of under a minute, the kind of figure such charts show for thin nitrile. Against 20 minutes of continuous contact, the glove was letting thinner through for nearly the entire task and holding it against the skin. The pattern on the hands fits that: worst on the right, the hand holding the wet gun.

The fix, in order. First the shop asks whether the task needs the solvent at all, which is the substitution question; see related: The Hierarchy of Controls on a Service Call. The gun takes a cleaner the manufacturer approves with a lower-hazard formula, and a gun-washing cabinet means hands are not in the solvent. For the cleaning that remains, the painter wears a laminate film liner under a fitted nitrile outer glove: the liner carries the permeation resistance across all three components and the outer glove gives grip. Both are changed after each cleanup, not reused the next day. The painter sees a clinician about the hands, who calls it irritant dermatitis; had it been allergic, the shop would also have looked at the glove itself and the products touched with bare hands.

The comparison case. The same crew uses the same 4 mil nitrile for wiping down primed trim with a damp rag of mineral spirits for a few seconds at a time. That glove is fine there: spirits are an aliphatic the table rates good for nitrile, the contact is splash rather than immersion, and the gloves go in the trash when the wipe-down is done. One glove, two tasks, two opposite answers, and the difference is the chemical family and the contact time, not the brand on the box.

References

• 29 CFR 1910.138, Hand Protection; 29 CFR 1926.95, Criteria for Personal Protective Equipment
• ASTM F739 and EN ISO 374-1, the permeation test method and the glove performance classification
• NIOSH, skin exposures and occupational skin disease resources
• See related: How to Choose a Glove from the SDS
• See related: Dose, Route, and the Exposure You Cannot See