Causes of Thickened Toenails

Thickened toenails may be caused by tinea pedis (athlete’s foot), a superficial fungal infection of the feet caused by dermatophytes, which can lead to nail thickening, rough skin, and erosion. Environmental factors may also contribute: prolonged exposure to hot, humid, and poorly ventilated environments—combined with unhealthy habits such as wearing non-breathable footwear and socks, and infrequent washing or changing of socks and shoes—can promote fungal growth and result in toenail thickening.