Discoloration of nails can signal a bacterial infection—and what that means for nail care.

Discoloration under or around the nail is more than a cosmetic oddity. It’s a signal that something in the nail bed or surrounding tissue isn’t behaving the way it should. In the world of nail care, the color you see can point toward health issues, and when it comes to discoloration, a bacterial infection is the strongest association you’ll hear about. That doesn’t mean other problems can be ignored, but it does mean that color change should be treated seriously and investigated promptly.

What color clues tell us about nail health

Let’s set the groundwork with a simple idea: nails don’t color themselves for no reason. When you see a change in hue, texture, or opacity, ask a few quick questions.

• Is the color green or has a greenish tint appeared? Green is the classic cue for a bacterial presence, especially when the nail bed is irritated or injured.

• Is the color dark or muddy, and is there a rough texture or a foul smell? Bacteria love damp, warm environments and can cause nail beds to thicken, yellow or brown, and even crumble at the edges.

• Is there accompanying redness, swelling, pain, or discharge? Those are red flags—signs that a deeper infection might be at work.

• Did the discoloration follow an injury, a manicure with questionable tools, or repeated exposure to moisture? Injury or poor tool hygiene can set the stage for infections to bloom.

Here’s the thing: while discoloration often signals a bacterial infection, it isn’t a foolproof diagnosis on its own. Trauma, allergies, or improper application of polishes and UV gels can also alter color—though these changes usually come with other telltale signs. The trick for professionals and clients alike is to read the full story the nail is telling, not just the color.

Green nails: a closer look

Green nails grab attention for good reason. Green nails are frequently linked to a bacterial infection, most notably caused by Pseudomonas aeruginosa. This particular bacterium thrives in moist environments and can sneak into the nail plate when there’s a tiny breach—think a small cut near the nail, a hangnail, or after a manicure where tools weren’t properly sanitized. The color you notice may appear as a greenish tint under the nail bed or creeping along the edges.

Several factors can contribute to this scenario:

• Persistent moisture under the nail from prolonged exposure to water or humid environments.

• Minor nail trauma that creates a tempting entry point for bacteria.

• Contaminated tools or surfaces in the salon if sanitation steps aren’t followed meticulously.

• Incomplete drying after treatments, or reopening of a previously cured, small crack in the nail plate.

If you observe green discoloration, don’t assume it’s nothing. It’s exactly the moment to pause a service, document concerns, and guide the client toward medical evaluation if symptoms persist or worsen. In the salon, you can help by ensuring your disinfecting protocol is solid and by teaching clients how to protect nails between visits.

Beyond green: what other colors can mean

Discoloration isn’t a one-color-only issue. Here’s a quick compass to keep in mind when you’re assessing nails:

• Allergy reaction or contact dermatitis: This can cause redness, itching, and sometimes blotchy color changes around the nail fold. The color shift is often accompanied by irritation or swelling, and it may improve when the offending product is removed.

• Injury or subungual hematoma: A bruise under the nail can turn nails various shades of blue, purple, or almost black. This is usually tied to trauma, like a squeeze or a heavy object hitting the nail. The nail may look thickened or separated as it grows out.

• Fungal infection: Fungi can yield yellow, white, or crumbly nails. The texture might be flaky or thickened, and the color change tends to be broader across the nail plate rather than a pinpoint area.

• Improper application: Overly thick layers of gel or polish can create a misleading color shift—often a dull hue rather than a bright, clean color. It can also trap moisture, which, in turn, might invite bacteria or fungus if the surface becomes compromised.

The bottom line: color is a clue, not a verdict. A clinician or dermatologist can provide a precise diagnosis, but a thoughtful nail tech can spot potential trouble early and guide clients toward safer care.

A practical, professional approach to nail health

For students and professionals entering the field, here’s a practical playbook you can apply every day. It blends sanitation, client education, and smart judgment without slowing you down.

• Sanitation is non-negotiable. Use tools that are either single-use or properly sterilized (think stainless steel implements run through a validated sanitizer or an autoclave). After every client, clean surfaces, bowls, and implements with an EPA-registered disinfectant. Replace porous items that can harbor bacteria.

• Separate the “no service” sign for infection signs. If you see redness at the cuticle, swelling, warmth, pain, or a foul odor, don’t push through with a manicure. Recommend medical evaluation, and avoid aggressive cuticle work or aggressive filing around the area.

• Wear protection. Gloves aren’t just for your safety—they reduce cross-contamination risk. If you’re working with a client who has a known infection, consider postponing cosmetic services until a medical professional clears it.

• Document and communicate. Note the color change, any accompanying symptoms, and whether there was recent trauma or tool issue. Share simple aftercare advice with clients: keep nails dry after washing, avoid tight gloves that trap moisture, and use breathable nail products if a sensitivity exists.

• Teach hygiene basics. For clients, explain that moisture between the nail and the skin is a hospitable place for bacteria. Suggest drying hands well, using breathable nail products, and giving nails a break from moisture-heavy activities after a session.

• Encourage early medical input when in doubt. If discoloration is coupled with pain, swelling, or spreading redness, a medical check is wise. The goal is to prevent a small issue from turning into a more serious infection.

Red flags that deserve a medical escalation

While most color changes are manageable with careful home care and professional hygiene, some signs warrant a medical referral. If any of the following show up, guide the client toward a healthcare provider:

• Severe pain, rapidly spreading redness, or warmth around the nail.

• Pus or oozing from the cuticle or nail bed.

• Nail changes that don’t improve or continue to worsen after a few weeks of good hygiene.

• A darkened, purplish or black nail after an injury that doesn’t start fading as the nail grows out.

These aren’t cosmetic issues anymore; they’re potential infections or injuries that require a professional medical assessment.

A quick care routine to support healthy nails

Even when nails look perfectly fine, a simple routine helps keep them resilient and less prone to discoloration.

• Keep nails clean and dry. Gentle washing, then thorough drying supports healthier nail beds.

• Trim and shape with care. Avoid overly aggressive filing that can create tiny microtraumas and open the door to bacteria.

• Hydrate, but avoid over-oiling the nail bed. Balanced moisture helps skin and nails stay flexible, which reduces cracks that invite bacteria in.

• Choose quality products and patches. When using gels or acrylics, pick reputable brands and ensure proper curing times to prevent heat buildup and peel-back that invites moisture and microbes.

• Schedule regular professional check-ins. A quick assessment every few weeks can catch early warning signs before they become overt problems.

A note to clients: partnering with your nail tech

Good nail health is a two-way street. Clients play a big role in noticing early changes and speaking up if something looks off. When you bring a “color change alert” to a tech’s attention, you’re helping protect your own nails and, frankly, supporting a safer salon culture. If you notice persistent discoloration after a service, document what happened and share it with your tech. Ask about the tools used, how they protected against cross-contamination, and what the aftercare plan looks like.

The takeaway for nail pros and students

Discoloration is a useful early warning signal. Among the possible causes, a bacterial infection is the strongest association, especially when green hues show up or when swelling and discharge accompany the color change. That said, it’s essential to consider the full picture—the injury history, moisture exposure, allergic responses, and the quality of tool sanitation all color the interpretation.

In practice, let color guide you, not dictate conclusions. Use it to prompt careful assessment, strict hygiene, and clear communication with clients. With a mindful approach, you can maintain nail health, deliver confident service, and minimize risks for both clients and your own professional well-being.

If you’re studying nail health, remember this streamlined rule of thumb: discoloration deserves attention, infection is a real possibility, and a thoughtful, hygienic approach is your best safeguard. Keep an eye on red flags, keep tools clean, and keep the conversation open with clients about how to protect their nails between visits. Nails don’t lie about health, but they do tell stories—and you’re the reader who can interpret them with skill and care.