Hair thinning, or diffuse thinning, can be caused by various diseases and conditions. Unlike localized hair loss, which affects specific areas, thinning typically involves a more widespread reduction in hair density.

Infections

Tinea Capitis: A fungal infection of the scalp that can lead to hair thinning or loss in patches, often accompanied by redness, scaling, and itching.

Folliculitis: Inflammation of the hair follicles caused by bacteria or fungi can result in hair thinning and breakage, especially if chronic or severe.