A hard little bump on the eggshell may be related to skin inflammation or a benign tumor.

Hard, small bumps on the skin can be caused by folliculitis, seborrheic keratosis, or skin tumors. If the bumps do not change significantly and are not accompanied by other symptoms, they are generally benign. However, if the bumps enlarge, change color, or ulcerate, you should seek medical attention promptly to rule out the possibility of malignancy. Patients are advised to observe changes in the bumps, have regular checkups, and seek professional medical help for diagnosis and treatment if necessary.

Folliculitis can cause local redness, swelling, and pain, and in severe cases, pustules may form. It's important to keep the area clean and dry, avoid scratching, and apply an antibiotic ointment topically.
Seborrheic keratosis is a common skin aging phenomenon that manifests as pale yellow to dark brown patches on the skin surface. It usually requires no special treatment, but if the bumps show signs of malignancy, they should be surgically removed as soon as possible.
Skin tumors include both benign and malignant types. Benign tumors include fibromas and lipomas, while malignant tumors include skin cancer. Diagnosis requires a biopsy for pathological examination. Benign tumors can be surgically removed, while malignant tumors require comprehensive treatment including radiotherapy and chemotherapy.
In daily life, pay attention to personal hygiene and avoid excessive friction or irritation of the affected area to prevent worsening of the condition. Also, avoid squeezing or puncturing the bumps to prevent infection or further deterioration.