Itchy thumbs can be triggered by dry skin, allergic reactions to soaps or cosmetics, and skin conditions such as eczema, according to Mayo Clinic. Thumb itching may also signify underlying conditions such as diabetes or nerve disorders.
Additional potential causes of itching skin can include insect bites, pregnancy and reactions to certain medications, according to MedlinePlus. Parasitic infections such as body lice and pinworms can also cause itching.
Itching skin is also a common symptom of psoriasis, a skin condition that causes skin cells to multiply rapidly, according to WebMD. Additional symptoms of psoriasis include joint discomfort, red skin patches, silver scales and pus-filled bumps on the skin. Individuals with psoriasis often experience symptoms on the palms of the hands and soles of the feet, however the condition can also affect the elbows, lower back, knees and face.
Treatment for itching skin depends on the cause of the condition and can include the use of over-the-counter antihistamine medications, dry skin lotions and prescription corticosteroid ointment, according to WebMD. Conditions such as eczema and psoriasis may require additional medical treatment. Over-scratching of the skin can lead to infection, so it is important for individuals with unexplained itching to determine the underlying cause.