Stains on the nails

Dermatologists who treat nail diseases

What usually explains a change in color in one or more nails and what are the signs that warrant a medical check-up?

Before reading: En skinpaths We distinguish between opinion and evidence. To write this content, we prioritized indexed medical sources and recommendations from scientific societies. At the end, you will find the complete bibliography for your reference.
Important: This article is for informational purposes only and does not replace medical advice. If you have any questions, persistent symptoms, or your condition worsens, consult a healthcare professional.

Summary in 60 seconds

• Nail stains are not a diagnosis in themselves: they are a clinical sign.
• They can be white, yellow, brown, black, green, or reddish.
• The most common causes include microtrauma, manicures, fungus, and blood under the nail after a blow.
• They can also appear due to nail inflammation, such as psoriasis, or due to pigment (melanin).
• A new dark line on a single nail deserves special and priority attention, especially if it widens or stains the surrounding skin.
• Yellow and thick nails often suggest onychomycosis, but it should be confirmed before starting long treatments.
• Pinpoint white spots are usually more related to local trauma.
• Color is a guide, but the number of affected nails, shape, speed of change, and associated symptoms are also important.
• If the injury changes, hurts, bleeds, lifts the nail, or appears without a clear explanation, it is wise to consult a specialist.

What is a biosimilar

“Nail discoloration” is a common way to describe changes in the color of the nail. This change can occur on the nail plate, underneath it (in the nail bed), or even on the surrounding skin. From a medical perspective, the finding may correspond to leukonychia (white spots), melanonychia (brown or black spots), pigmentation due to infection, blood under the nail, or changes secondary to inflammation. Singal 2020 Iorizzo 2022

A stain on the nail is not a diagnosis: the color is indicative, but the medical history and examination are what really define the problem.

Why do they appear?

The causes are better understood if we think of them in four main groups. The first is the traumaImpacts, repeated friction, nail biting, or aggressive manicures can leave white spots, lines, or blood under the nail. The second is... infectionsespecially fungi, which often turn the nail yellow, white, or brown and also thicken or make it brittle. The third is the inflammationsuch as nail psoriasis, which can produce "oil drop" spots, dots, blood lines, and partial detachment. The fourth is the pigmentespecially melanin, which can form a brown or black band; most of these bands are not melanoma, but some do require further investigation. Iorizzo 2022 Leung 2020 Singal 2020

In a smaller group of patients, the color can also change due to bacteria. The so-called "green nail" is often associated with Pseudomonasespecially when the nail is detached or frequently remains moist. Much less often, some extensive white lesions or certain multiple splinter hemorrhages may be associated with systemic problems and warrant further evaluation. Haber 2016

What do they look like?

small white spots They are often seen as isolated spots and, in many cases, are related to microtrauma or manicure habits. diffuse yellow or whitish They are often accompanied by thickening, brittleness, or subungual debris, which suggests a fungal infection. brown or black They can appear as a vertical band or as a more diffuse area; sometimes they are due to benign pigment and other times they require ruling out melanoma. greenish suggest bacterial colonization. reddish, purple, or dark brown The bumps that appear after a blow may correspond to blood under the nail and, over time, they usually move towards the free edge as the nail grows. Iorizzo 2022 AAD 2025 AAD 2021

In what diseases or conditions do they usually occur?

The following can be mentioned as a guide:

1. Very frequent

• Microtrauma and manicure: white spots or small color changes after minor bumps, friction, biting nails or manipulating cuticles. Iorizzo 2022
• Onychomycosis (fungi): yellow, white or brown nails, with thickening, brittleness, detachment or debris under the nail. Leung 2020 Fraser 2021
• Subungual hematoma: reddish, purplish, brown or black stain after a clear blow or repeated trauma.

2. Frequent

• nail psoriasis: dimples, "oil drop" spots, blood lines, nails that peel or become brittle. AAD 2023
• Benign longitudinal melanonychia: brown or black band, sometimes related to melanocytic activation, drugs, friction, or individual pigmentary characteristics. Singal 2020
• Splinter hemorrhages: thin reddish-brown lines, with a traumatic cause in many cases, although they can also be seen in psoriasis and other inflammatory conditions. Haber 2016

3. Infrequent

• Green nail caused by Pseudomonas: typical in wet, detached nails or with chronic paronychia. Chiriac 2015
• Leukonychia associated with systemic disease: more relevant when the white coloration affects several nails or almost the entire nail, not as a simple isolated spot. Iorizzo 2022
• Subungual melanoma: rare, but clinically very important due to its diagnostic and prognostic impact. Darmawan 2022 AAD 2021

When to consult?

Consult a dermatologist if you notice any of these signs:

• A new brown or black streak on a single nailespecially if it widens over time.
• Pigment that reaches the skin around the nail (for example, the cuticle)
• Pain, bleeding, lump, nail that splits or lifts without a clear cause.
• A dark stain that does not "move" outwards as the nail grows.
• Yellow, thick, or brittle nails that lasts for months or is accompanied by pain.
• Green Color with bad odor, persistent dampness, or swelling around it.
• Several white or altered nails along with other general symptoms or known illnesses.
• Diagnostic doubtsIn the case of nails, letting time pass without a clear diagnosis can delay the correct treatment. AAD 2021 BAD 2026 Darmawan 2022

What NOT to do?

It's unwise to assume that every yellow nail is "just a fungal infection" or that every black streak is caused by an injury. Aggressive scraping, piercing the nail at home, covering a new, changing lesion with polish or gel, or starting oral antifungal medication without a confirmed diagnosis are also not good ideas. In cases of onychomycosis, several guidelines recommend confirming the diagnosis before prescribing systemic treatment, as other diseases can present with very similar symptoms. AAD 2025 Fraser 2021

Treating a yellow nail or a dark band "blindly" can delay the correct diagnosis.

What does a dermatologist usually do?

The first thing is a targeted medical historyNote when the spot appeared, if there was any injury, if it changes size, if it affects one or more nails, if there is pain, if you are taking any medications, if you have psoriasis, previous infections, or if you are frequently exposed to water. Then check all nailsnot just the most visible one. Singal 2020 Darmawan 2022

If the lesion is pigmented, you can use dermatoscopy or onychoscopy to assess the color pattern and decide if it appears benign or suspicious. If a fungal infection is suspected, further testing is usually requested. nail clipping or sample For study. If the white pattern is extensive or affects many nails, sometimes additional layers are added. complementary analysesAnd if there are warning signs of melanoma or another tumor, further investigation may be necessary. nail biopsy. Fraser 2021 Darmawan 2022 Iorizzo 2022

FAQ

Do white spots mean a calcium deficiency?

• This is not usually the primary explanation. In most isolated white spots, the most likely cause is minor trauma to the nail matrix or manicure habits. Iorizzo 2022

Is a black line on the nail always melanoma?

• No. Many dark bands are benign. Even so, a new band on a single nail that grows, widens, or pigments the surrounding skin should be evaluated as a priority. Singal 2020 AAD 2021

Are yellow nails usually caused by fungus?

• Often, yes, especially if they are also thick, brittle, detached, or have debris underneath. But psoriasis, trauma, and other causes can also look similar, so it's often best to confirm. Fraser 2021 AAD 2025

How long does it take for the white spots to disappear?

• If they are caused by minor trauma, they usually move outwards as the nail grows. On the fingers, this can take several months. Iorizzo 2022

Can a stain from a bump or knock look worrying?

• Yes. A subungual hematoma can appear very dark and be mistaken for other causes. The progression helps: after the trauma, the discoloration usually moves toward the distal edge as the nail grows. DermNet, subungual hematoma

Why does a fingernail turn green?

• The typical cause is colonization by Pseudomonas, favored by humidity, onycholysis or chronic inflammation around the nail. Chiriac 2015

Can I cover the stain with nail polish while I keep an eye on it?

• It's not ideal. To properly assess a pigmented lesion, it's important to be able to see its actual evolution and decide if further investigation is needed. AAD 2021

Bibliography and sources

• Singal A, Bisherwal K. Melanonychia: Etiology, Diagnosis, and Treatment. Indian Dermatol Online J. 2020;11(1):1-11.
• Iorizzo M, Starace M, Pasch MC. Leukonychia: What Can White Nails Tell Us?. Am J Clin Dermatol. 2022;23(2):177-193.
• Leung AKC, Lam JM, Leong KF, Hon KL, Barankin B, Leung AAM, et al. Onychomycosis: An Updated Review. Recent Pat Inflamm Allergy Drug Discov. 2020;14(1):32-45.
• Frazier WT, Santiago-Delgado ZM, Stupka KC II. Onychomycosis: Rapid Evidence Review. Am Fam Physician. 2021;104(4):359-367.
• Darmawan CC, Ohn J, Mun JH, Kim S, Lim Y, Jo SJ, et al. Diagnosis and treatment of nail melanoma: a review of the clinicopathologic, dermoscopic, and genetic characteristics. J Eur Acad Dermatol Venereol. 2022;36(5):651-660.
• Haber R, Khoury R, ​​Kechichian E, Tomb R. Splinter hemorrhages of the nails: a systematic review of clinical features and associated conditions. Int J Dermatol. 2016;55(12):1304-1310.
• Chiriac A, Brzezinski P, Foia L, Marincu I, Pinteala T, Solovan C, et al. Chloronychia: green nail syndrome caused by Pseudomonas aeruginosa in elderly people. Clin Interv Aging. 2015;10:265-267.
• American Academy of Dermatology Association. How to check your nails for melanoma [Internet]. 2021 [cited 2026 Apr 19].
• American Academy of Dermatology Association. Nail fungus: Signs and symptoms [Internet]. 2025 [cited 2026 Apr 19].
• American Academy of Dermatology Association. Nail fungus: Diagnosis and treatment [Internet]. 2025 [cited 2026 Apr 19].
• American Academy of Dermatology Association. What is nail psoriasis, and how can I treat it? [Internet]. 2023 [cited 2026 Apr 19].
• British Association of Dermatologists. Fungal nail infections [Internet]. 2026 [cited 2026 Apr 19]