The possible cause of very hard pimples on the face is acne. It is usually treated with medication, phototherapy, and adjuvant therapy. 1. Medication: Topical medications include vitamin A acid cream, benzoyl peroxide, and erythromycin ointment. Systemic medications use doxycycline, minocycline, and so on. You can also use isotretinoin, spironolactone and other anti-androgen drugs, prednisone and other glucocorticoids. 2. Phototherapy: the use of LED blue light, photodynamic therapy, and topical 5-amino ketoglutaric acid enriched in the follicular sebaceous gland units. 3. Adjuvant therapy: common exfoliators include fruit acid, salicylic acid, hydroxyacetic acid and trichloroacetic acid. The appearance of very hard pimples on the face, you need to seek medical attention as soon as possible. Do not take medication on your own to avoid serious complications.