Why does my thumbnail keep splitting, causing onychoschizia (nail splitting)?

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From the Guidelines

Your thumbnail splitting, causing onychoschizia, is likely due to a combination of factors including nutritional deficiencies, and supplementing with biotin can help strengthen brittle nails. To address this issue, consider the following:

  • Keeping your nails moisturized with a nail oil or hand cream containing ingredients like jojoba oil, vitamin E, or shea butter, as dryness can exacerbate nail splitting 1.
  • Wear gloves when doing dishes, cleaning, or working with chemicals to protect your nails from harsh substances.
  • Taking a biotin supplement, as it has been successful in the treatment of brittle nails (onychoschisis) 1, with a recommended daily dose of 2,500-5,000 mcg.
  • Maintaining a balanced diet rich in protein, iron, and zinc, as these nutrients are essential for healthy nail growth.
  • Avoid using your nails as tools for opening packages or scratching surfaces, as this can cause trauma and lead to nail splitting.
  • If you notice yellowing, thickening, or pain around the nail, consult a dermatologist as this could indicate a fungal infection requiring prescription antifungal medication. Nail splitting often occurs because the nail plate consists of layers of keratin that can separate when damaged or dehydrated, so consistent protection and moisturizing are key to allowing your nail to grow out healthy and intact, and biotin supplementation can play a crucial role in this process, as supported by the study published in the American Journal of Clinical Dermatology 1.

From the Research

Causes of Onychoschizia (Nail Splitting)

  • Onychoschizia, or nail splitting, can be caused by various factors, including direct injury to the nail plate or matrix insult 2.
  • Longitudinal nail splitting may be caused by tumours, inflammatory diseases, traumas, congenital, and systemic disorders 2.
  • The most frequent aetiologies of longitudinal nail splitting are tumours (45.6%), inflammatory diseases (26.3%), and traumas (19.3%) 2.

Specific Causes of Thumb Nail Splitting

  • A case study reported a 56-year-old patient with longstanding central splitting of the nail plate of his right thumb, which was diagnosed as median canaliform nail dystrophy 3.
  • Another study found that the fingernails, especially the thumb, are more frequently affected by longitudinal nail splitting than toenails 2.

Treatment Options for Nail Splitting

  • Phenol alcohol partial nail matricectomy has been proven to be a simple, effective, and reproducible treatment with excellent cosmetic results for laterally located split nails 4.
  • Terbinafine has been shown to be effective in treating onychomycosis, including in high-risk populations and in patients with nondermatophyte infections 5, 6.

Factors Contributing to Nail Splitting

  • Nail splitting can be caused by alteration of the nail matrix integrity, resulting from matrix stretching by an underlying tumour or impairment of the keratinization process by inflammatory diseases 2.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Causes of longitudinal nail splitting: a retrospective 56-case series with clinical pathological correlation.

Journal of the European Academy of Dermatology and Venereology : JEADV, 2022

Research

[A man with thumb nail abnormalities].

Nederlands tijdschrift voor geneeskunde, 2015

Research

The treatment of the splitting nail with phenol alcohol partial nail matricectomy.

Dermatologic surgery : official publication for American Society for Dermatologic Surgery [et al.], 1996

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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