Etrasimod Arginine Blue is an oral tablet taken in a single dose. It contains the active ingredient etrasimod, which is being studied to see how it moves through the body and is cleared. In this trial healthy volunteers swallow the tablet while fasting, and researchers measure how much of the drug appears in tiny blood samples.

Tasso micro‑sampling device is a small, wearable tool that collects tiny drops of blood from the participant’s arm. Participants can place the device on themselves to obtain blood samples without needing a nurse or clinic visit. The collected samples are used to measure the amount of etrasimod in the blood.

Wearable monitoring devices are sensors that participants wear, such as patches or wristbands, that continuously track vital signs like heart rate, temperature, and activity. These devices help the study team watch for any safety concerns or side effects after the tablet is taken.

Ulcerative colitis – a long‑lasting inflammation of the inner lining of the colon that creates ulcers and can cause diarrhea, rectal bleeding, and abdominal pain. The inflammation usually starts in the rectum and may spread continuously upward through the colon. Symptoms often come and go in periods called flares and remissions. Over time the disease can become more extensive, affecting larger parts of the colon. Severe inflammation may lead to narrowing of the colon and changes in bowel habits.

Alopecia areata – an autoimmune disorder in which the immune system attacks hair follicles, causing smooth, round patches of hair loss on the scalp or other body areas. In some people the patches stay small, while in others they expand or progress to total scalp loss (alopecia totalis) or loss of all body hair (alopecia universalis). The condition can appear suddenly and may recur after regrowth. The pattern and speed of hair loss vary widely between individuals.

Atopic dermatitis – a chronic, itchy skin condition that often begins in childhood and appears as red, inflamed patches on the flexural areas such as elbows and knees. The rash may flare up repeatedly, becoming more widespread or thickened with repeated scratching. Over time the skin can become dry, cracked, and lichenified (thickened). The disease course is characterized by periods of worsening symptoms followed by calmer phases.

Eosinophilic esophagitis – a long‑term allergic inflammation of the esophagus marked by a buildup of eosinophils, a type of white blood cell. It leads to difficulty swallowing, feeling that food is stuck, and occasional food blockage. Repeated inflammation can cause the esophagus to narrow or develop rings. Symptoms often worsen gradually as the condition persists.