This is a Phase I, single-site study to evaluate the sensitization potential of topically applied ATx201 GEL, 2% and 4%, along with a placebo control, in healthy human subjects.

Inclusion Criteria:

• Good general health
• Body Mass Index no less than 19.0 and no greater than 36.0 kg/m² (inclusive).
• Demonstrates a Fitzpatrick skin score of I - IV
• Female subjects must agree to use acceptable contraceptive methods from the Screening Visit through 90 days after the End of Study (EOS) Visit; or postmenopausal status with no menses for at least 1 year prior to the Screening Visit.
• Willing to refrain from excessive consumption of sodium in food or beverage 48 hours prior to Day 1 through EOS Visit.
• Willing to shower using the same non-medicated soap/cleansers, and abstain from excessive sun exposure (including tanning salons) from the Screening Visit through EOS Visit.

Exclusion Criteria:

• Reports a history of diabetes mellitus, clinically significant asthma (acceptable if no episode within 5 years prior to Day 1), or currently diagnosed with hypertension or circulatory disease.
• Reports use of any oral, nasal or topical corticosteroids, or oral or topical retinoids (other than Vitamin A at normal dietary amounts)
• Reports a significant history of allergy to soaps, lotions, emollients, ointments, creams, cosmetics, adhesives, or latex.
• Reports a history of significant skin conditions or disorders such as psoriasis, atopic dermatitis, etc.
• Reports a history of significant dermatologic cancers.
• Displays an obvious difference in skin color between upper arms or upper back or the presence of a skin anomaly
• Reports smoking or use of tobacco or nicotine delivery products within 14 days prior to Day 1 through EOS Visit.
• Presence of any clinically significant results from laboratory tests and vital signs assessments, as judged by the Investigator.
• A female who is pregnant, lactating, breastfeeding, or intends to become pregnant over the course of the study.
• Reports a history of drug or alcohol addiction or abuse within the past year.
• Reports having donated blood or plasma within 48 hours prior to Day 1 through EOS Visit.
• Subject exhibits excessive hair density on the upper arms or back such that patch adhesion could be compromised.
• Subject reports undergoing hair depilation (e.g. chemical, laser, physical) within 30 days prior to Day 1 through EOS Visit.