The short answer for a Syrian hamster
Syrian hamsters sleep deeply through the day and live at night, so check yours after he wakes naturally: bright, wide eyes, a dry nose, silent breathing, even front teeth, flat empty cheek pouches, a clean dry tail end, and energetic running and burrowing. Syrians are solitary and can be startled by daytime handling, which makes a calm evening check both kinder and more accurate. You are looking for changes against his own busy baseline: a Syrian who skips the wheel, leaves food unpouched, or sits hunched in a corner is showing you the first chapter of a problem.
Watch the night routine first
Spend a few minutes watching before you lift him. A well Syrian emerges, stretches, grooms, stuffs his pouches with food, and runs the wheel in long, steady bouts. Notice whether the wheel stays silent all evening, whether the food store in his nest grows as usual, and whether droppings in the bedding look firm and plentiful. Listen for sneezing, clicking, or wheezing as he moves, and look for wetness around the nose or eyes stuck partly shut. Changes in this routine are often visible a day or two before anything can be felt in the hand.
Coat, skin, and the hip scent glands
Let him walk into a jug or your cupped hands and settle on a towel. The coat, long in some Syrians, should be free of mats, tangles that pull at the skin, bald patches, and scabs; part it gently to check the skin beneath for flaking or redness. On each hip you will find a darker, sometimes slightly damp-looking patch of skin and fur: these are normal scent glands Syrians use for marking, not wounds, though a gland that becomes swollen, crusty, or sore-looking deserves a vet's opinion. Feel carefully along the body for lumps, and look at the belly for swelling or a dirty, wet underside.
Pouches, teeth, and the tail end
Cheek pouches should empty fully; watch him unload into his store and check that both sides go down flat and stay flat. A pouch that remains bulging, or a hamster pawing at his face and drooling, suggests something is stuck or the pouch lining is injured, which needs veterinary help rather than home probing. Glance at the front teeth as he takes a treat: they should meet evenly and look unbroken. Finally, look at the tail end. A wet, soiled rear, especially with watery droppings and a hunched, miserable posture, is an emergency in a young Syrian and urgent at any age; do not wait overnight to see if it dries.
Weigh, record, and know the urgent signs
Weigh him weekly in a small container on a kitchen scale, because steady loss in a hamster who still appears round under his coat is easy to miss by eye. Contact a vet promptly for laboured or noisy breathing, a persistently swollen pouch, teeth that grow uneven or break, a lump that appears or enlarges, or a hamster who stops eating and hides through his usual active hours. Bleeding, a prolapse, or a wet tail end means going the same day. Writing each evening check and weekly weight into KinsLe through the Pet Passport builds the baseline that turns a vague worry into clear information for the vet.