Steatocystoma multiplexhttps://en.wikipedia.org/wiki/Steatocystoma_multiplex
Steatocystoma multiplex is a benign, autosomal dominant, congenital condition that results in multiple cysts on the body. The cysts are usually small (2–20 mm) but can reach several centimeters in diameter. They appear as soft‑to‑firm, semi‑translucent papules and contain an oily, yellow fluid.

Onset typically occurs at puberty, likely due to hormonal stimulation of the pilosebaceous unit. Lesions most commonly appear on the chest and may also be found on the abdomen, upper arms, axillae, and face. In some individuals, cysts can develop over the entire body.

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  • When it is observed on the arm or neck, it appears as a small, hard, subcutaneous cyst that is usually asymptomatic.
    References Steatocystoma Multiplex 38283021 
    NIH
    Steatocystoma multiplex (SM, also known as steatocystomatosis, sebocystomatosis, or epidermal polycystic disease) is a rare benign intradermal true sebaceous cyst of various sizes. Clinically, SM presents as asymptomatic, numerous, round, smooth, firm, mobile, cystic papules, and nodules. The lesions are uniform, with a size of a few millimeters to centimeters along the long axis. The superficial lesions are yellowish, and deeper lesions tend to be skin-colored. The fluid in SM is odorless, oily, clear or opaque, milky or yellow. The overlying epidermal skin is often normal, with no central punctum. SM can occur anywhere in the body but is more frequently seen in areas rich in pilosebaceous units such as the trunk (especially the presternal region), neck, scalp, axilla, proximal extremities, and inguinal region.
     Steatocystoma multiplex - Case reports 14594591
    A 25-year-old man came in with a skin condition on his arms, chest, and abdomen. He had been with painless lumps for 20 years, starting on his chest and spreading to his arms over the past 7 years.