According to WebMD, cracked skin on the thumbs occurs when the delicate skin of the hands loses moisture. Cracked skin on the fingers and thumbs is common during the winter months due to dry air and cold temperatures. Wearing wet gloves in the winter can also cause cracked skin on the thumbs, as the moisture trapped inside the glove can irritate the skin, leading to cracking and sores.
The National Eczema Association explains that cracked skin is a common symptom of hand eczema, a common skin condition that occurs when the skin comes in contact with chemical irritants and allergens. Hand eczema is also caused by genetic factors. Additional symptoms of hand eczema include redness, itching and severe dryness. Cracks on the skin are also referred to as fissures. Eczema is not contagious and can be treated with corticosteroid creams.
According to Medline Plus, fissures on the skin of the hands often occur with irritant dermatitis, a condition in which the skin reacts to allergens and certain chemicals that are found in hair products, cosmetics, lotions and soaps. Allergic dermatitis is treated with moisturizers and corticosteroid creams. Avoiding contact with suspected chemical irritants can help to minimize the chance of future inflammation.