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Undecylenic Acid disrupts the cell walls of dermatophyte fungi — the same family of organisms behind toenail fungus, jock itch, and athlete's foot. At the OTC maximum strength of 25%, it works to kill existing fungal growth while preventing new colonies from taking hold around the nail.
The brush-pen applicator paints a thin, even layer directly onto the nail surface and into the cuticle, edges and surrounding skin — the exact crevices where fungus hides and cotton swabs miss.
Active Ingredient
Undecylenic Acid 25% w/w (OTC antifungal).
Inactive Ingredients
Caprylic Acid, Ethanol, Propylene Glycol, Tocopheryl Acetate (Vitamin E), Melaleuca Alternifolia (Tea Tree) Leaf Oil, Lavandula Angustifolia (Lavender) Oil, Eucalyptus Globulus Leaf Oil, Salicylic Acid, Camphor.
Maximum-strength 25% Undecylenic Acid in a precise brush-pen — paints OTC antifungal directly onto and around fungus-damaged nails.
"For best results, plan on twice-daily application for 4–6 months. Nails grow slowly, so a fungal nail needs that long to be fully replaced by clear growth. The pen format and 25% undecylenic acid concentration make it the most realistic at-home protocol I recommend."
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40+ Board-Certified Podiatrists use the Antifungal Nail Pen in their patient care routines
In short supply — we restock weekly
Each batch of the 25% Undecylenic Acid formula is filled and quality-checked in small lots, so they sell out fast.
Undecylenic Acid disrupts the cell walls of dermatophyte fungi — the same family of organisms behind toenail fungus, jock itch, and athlete's foot. At the OTC maximum strength of 25%, it works to kill existing fungal growth while preventing new colonies from taking hold around the nail.
The brush-pen applicator paints a thin, even layer directly onto the nail surface and into the cuticle, edges and surrounding skin — the exact crevices where fungus hides and cotton swabs miss.
Active Ingredient
Undecylenic Acid 25% w/w (OTC antifungal).
Inactive Ingredients
Caprylic Acid, Ethanol, Propylene Glycol, Tocopheryl Acetate (Vitamin E), Melaleuca Alternifolia (Tea Tree) Leaf Oil, Lavandula Angustifolia (Lavender) Oil, Eucalyptus Globulus Leaf Oil, Salicylic Acid, Camphor.
Henry B.
I tried everything — Vicks, tea tree oil, the stuff from the pharmacy, you name it. Finally tried this pen and after a few months my toenails actually look like toenails again. Had to be patient but it definitely paid off.
Emily W.
Don't waste time with other products or medications like I did. I've tried countless creams, polishes and prescriptions over the years. The brush makes this so much easier to apply consistently — and consistency is the whole game with nail fungus.
Anna L.
I thought I'd be stuck hiding my feet forever. After consistent twice-daily use I'm wearing sandals again — for the first time in years. The pen applicator gets right into the cuticle where the discoloration starts.
The Antifungal Nail Pen doesn't just mask the discoloration — it targets the dermatophyte fungi at the source. Here's exactly how.
Nail fungus can be triggered by many factors: fungal spores, sweaty shoes, gym floors, public showers, chronic conditions like diabetes, or simply slow nail growth as you age.
What they all have in common: the dermatophyte family of fungi colonizing the nail bed under the hardened nail plate, where most creams and drops can't reach.
Untreated, the fungus spreads laterally — yellowing, thickening, and crumbling the nail over months. The earlier you act, the faster the new clear nail can grow in.
The pen delivers 25% Undecylenic Acid — the FDA-recognized OTC antifungal maximum strength — directly to where dermatophytes live.
The brush applicator paints precisely into the cuticle, the lateral folds, and the surface of a filed-back nail. The alcohol-based vehicle thins as it dries, carrying the active deep into the crevices instead of running off the nail surface.
No spills. No cotton swabs. No fingers spreading fungus from one nail to the next.
With consistent daily use, most users see a clearer, healthier nail growing in from the base within 8–12 weeks.
Full replacement of an infected nail takes 4–9 months for fingernails and up to 12 months for toenails — because nails grow slowly. Document with photos every two weeks; the change is gradual but clearly visible when you compare side-by-side.
If you don't see new clear growth at the base in 140 days, we'll refund you.
"The reason most at-home antifungals fail is the vehicle, not the active. This pen puts 25% undecylenic acid exactly where the dermatophyte lives — the cuticle, the lateral folds, and the surface of a filed-back nail. It's the first OTC application I've seen that actually behaves like a clinic protocol."
Step 1: Document your nail
Photograph the affected nail before you begin, then once a week. Fungal nail change is gradual — comparison photos make the progress obvious.
Step 2: Apply twice daily
Morning and night, for 140 days. Brush a thin layer onto the nail, cuticle and surrounding skin. Skipping days lets the fungus recolonize.
Step 3: Stick with it for 140 days
Nails grow slowly — visible new clear growth shows up in weeks, full replacement of an infected nail can take months. If you commit to consistent daily use and don't see a difference within 140 days, we'll refund you.
Most users see a clearer, healthier nail growing from the base within 8–12 weeks of twice-daily use. Full replacement of an infected nail takes 4–9 months for fingernails and up to 12 months for toenails, because nails grow slowly. Document with photos every 2 weeks — the change is gradual.
Yes. 25% Undecylenic Acid is the FDA-recognized OTC maximum for topical antifungal use on nails and skin. It's available over the counter specifically because it's safe for unsupervised at-home use. Mild redness or tingling on the surrounding skin is normal; if it persists, reduce to once daily.
The pen targets dermatophyte fungi — the family of organisms responsible for the majority of nail fungus, athlete's foot, and jock itch. It's designed for discolored, thickened, brittle nails on fingers or toes. It won't treat bacterial paronychia or yeast infections (those look different — see a doctor if the nail folds are red, swollen and painful).
Two reasons. Vehicle: the alcohol-based solution thins as it dries, carrying the antifungal into the crevices where fungus lives. Applicator: the brush paints precisely along the cuticle and lateral folds, instead of dripping off the nail surface or smearing fungus between nails with your finger.
We offer a 140-day money-back guarantee. If you use the pen consistently twice daily for 140 days and don't see new clear nail growth at the base of the affected nail, email our support team and we'll refund you in full — no return of the pen required.
Yes — that's the brush pen's biggest advantage over finger-applied creams. Treat each affected nail with the same pen. The undecylenic acid and the alcohol vehicle prevent cross-contamination between nails. Painting at the same applicator angle keeps the dose consistent.
Strongly recommended. Filing back the dead, fungus-damaged surface lets the antifungal reach the nail bed where the active infection is. Use the Precision Nail Drill once a week — file down to a thinner, lighter-colored layer, then apply the pen. Without filing, the antifungal has to penetrate hardened keratin.
Possibly. Continue twice-daily use until the entire infected nail has grown out and been replaced by clear nail. Stopping too early leaves residual fungus in the nail bed. After replacement, many users switch to a maintenance routine — once-daily or 3x/week + the Antifungal Foot Balm to keep the surrounding skin inhospitable to fungus.
Yes, but for active treatment we recommend going polish-free until the nail is fully replaced. Polish forms a barrier that traps moisture against the nail bed — exactly the environment fungus thrives in. Once the nail is clear, occasional polish use is fine.
Consult your doctor before use. Undecylenic acid has a long safety record for topical OTC use, but as with any topical medication during pregnancy or breastfeeding, get clearance from your healthcare provider.
Diabetic foot issues require medical supervision. The active is safe, but nail and skin issues in diabetics can mask more serious circulatory problems. Talk to your podiatrist or physician before adding any antifungal to your routine.
No staining — the formula dries clear. There's a faint medicinal scent (tea tree + camphor) that fades in 60 seconds as the alcohol evaporates. Most users prefer it to the smell of prescription topicals.
Undecylenic Acid is an FDA-recognized OTC antifungal active ingredient per the OTC Antifungal Drug Products monograph (21 CFR 333). Our formulation uses the maximum OTC strength of 25%. The product is manufactured in an FDA-registered facility under cGMP standards.
