The thumb suddenly became very itchy and swollen.

Generally, sudden itching and swelling of the thumb may be caused by allergies, insect bites, hand eczema, atopic dermatitis, psoriasis, etc., and different treatment approaches are required depending on the underlying cause. If symptoms persist or worsen, it is recommended to seek medical attention immediately. Detailed analysis is as follows:

1. Allergies: Contact with allergens such as pollen, animal hair, or certain foods may trigger an allergic reaction, leading to itching and swelling of the thumb. Medications such as cetirizine hydrochloride tablets or loratadine tablets can be taken under medical guidance.

2. Insect bites: Bites from insects can also cause localized skin itching and swelling, including on the thumb, possibly accompanied by bite marks or redness. Symptoms usually resolve on their own.

3. Hand eczema: Hand eczema is a common skin condition characterized by dry, itchy, red, peeling, or even ulcerated skin on the fingers. It may affect the area of the thumb. Topical treatments such as desonide cream or hydrocortisone cream can be used under a doctor's supervision.

4. Atopic dermatitis: Atopic dermatitis is a non-contagious chronic inflammatory skin disease commonly presenting with itching, redness, and rashes. Itching and swelling of the thumb may be one manifestation. Treatments such as calamine lotion or mupirocin ointment can be used as directed by a physician.

5. Psoriasis: Psoriasis is a common skin disorder characterized by red patches with scaly plaques, which may be accompanied by itching and swelling. It can occur around the fingers and nails. Medications such as ibuprofen sustained-release tablets or methotrexate tablets may be prescribed to help manage symptoms.

A light diet is recommended; avoid spicy or irritating foods such as garlic, hot pot, wasabi, etc. Adequate rest should be maintained, and excessive fatigue should be avoided to prevent adverse effects on overall health.