Hamsters are common household pets.  They are inexpensive, friendly, and fairly easy to care for.  Hamsters are rodents, often referred to as "pocket pets" because of their small size.

Background
Hamsters are somewhat peculiar rodents with large cheek pouches and short, stubby tails.   They have gained popularity as pets and research animals since the 1930's.   The Syrian hamster's (Golden hamster) wild habitat extends through the Middle East and south eastern Europe.  In 1930, a litter of eight baby hamsters was taken to Israel and raised as research animals.  Virtually all domesticated hamsters sold as pets today are descendents of three survivors of this litter.  Hamsters were first introduced to the United States in 1938.  Since their domestication, several color varieties of Syrian hamsters have become common due to selective breeding.  The three basic groups that now exist and are popular as pets include:
the Golden hamster
the colored, short-haired Fancy hamster, and
the long-haired Teddy Bear hamster.

Occasionally, other species of hamsters may be encountered, but they are much less common than the Syrian Hamster.  The smaller dark brown Chinese hamster (Dwarf hamsters) are often used in biomedical research and are sometimes acquired as pets.  These hamsters are recognizable by their small size, dark brown color, and black stripes over their backs.  Armenian (gray)  and European hamsters are two other species occasionally used in research but seldom kept as pets. 

Hamsters are small, soft animals with a fair temperament.   They tend to be active at night and like to sleep during the day.  They can be cranky when abruptly awakened, so caution is advised when handling them at this time.   Hamsters love to dig, burrow, and chew.

Hamster Statistics:

Life span: 2 - 3 years
Cage temperature range: 65-80F
Relative humidity range : 40-70%
Breeding age: 6-10 weeks for females, 10-14 weeks for males
Estrous cycle: 4 days
Gestation period: 15-16 days
Litter size: 5-10
Weaning age: 21-25 days

Diet

As with any pet, good-quality food and clean, fresh water must be provided at all times, In the wild, hamsters feed on leaves, seeds, roots, various fruits, and insects.   Pelleted rodent rations containing 18 to 22% protein are recommended for feeding hamsters in captivity.  These foods are typically processed as dry blocks or pellets designed specifically for rodents.  Seed diets are also formulated and sold for hamsters, but these diets should only supplement the basic rodent pellet as a treat. Many hamsters prefer sunflower-based diets to pellets, but these seeds are low in calcium and high in fat and cholesterol.  When fed alone, seed diets can lead to obesity and potential nutritional deficiencies.  Other supplements to the diet may include sugarless breakfast cereals, whole wheat pasta, cheese, and fresh fruits and vegetables.   However, these items should all be fed in moderation.

Hamsters eat approximately 12 grams of food daily and usually ingest the majority of this food during the night.  Hamsters will often hoard their food in a corner of their cage making it seem as though they are eating more than they really do.

Water should be provided in water bottles equipped with sipper tubes.  This method of providing water also helps keep the water free from contamination.  Always make sure that the tubes are positioned low enough to allow your hamster easy access.  Inadequate water consumption can lead to infertility, lower bodyweight and eventually death.  The average hamster drinks approximately 10 milliliters of water per 100 grams of bodyweight.  although this amount is only a fraction of the total amount of water in the bottle, the bottle should be emptied, cleaned and refilled with fresh water daily.

Handling

Hamsters handled frequently from a young age usually remain docile and seldom bite.   A hamster can be picked up gently by cupping it in one or both hands and holding it against your body.  Beware that even docile hamsters may bite if surprised or abruptly awakened from sleep.

Hamsters that do not receive much attention and handling may be more apprehensive and aggressive.  Any animal whose personality is not know fully must be approached cautiously.  Using a small towel or gloves can help in capturing and restraining such a pet.  Another method of capture involves coaxing the animal into a container (such as a can or tube) which can then be removed from the cage.   Once removed from the cage a biting pet can be restrained by grasping a large amount of skin at the scruff of the neck.  When handling hamsters in this manner, as much skin as possible must be grasped because their skin is very loose.  If lightly scruffed, the hamster can easily twist around and bite the handler.

Housing

Several types of cages are suitable for housing small rodents.  Many of these units come equipped with cage furniture such as exercise wheels, tunnels, and nest boxes.  Such accessories, as well as sufficient litter depth within which to burrow, are desirable for the pet's psychological well-being.  Cages should be constructed with rounded corners to discourage chewing.  Hamsters will readily chew through wood and light plastic.  Wire, stainless steel, durable plastic, and glass are recommended caging materials.  Glass and plastic containers, however, may reduce ventilation and lead to problems with temperature and humidity requirements.

Optimal temperature range for hamsters is between 65 and 80F, with babies doing best at 70 to 75F.  The relative humidity should be between 40% and 79%.  Glass and plastic materials can make suitable cages if at least one side of the enclosure is open for air circulation.  The enclosure should be escape-proof.

Hamsters thrive in solid-bottom cages with deep bedding and ample nesting material.  Adult hamsters require a minimum floor area of 19 square inches and a cage height of at least 6 inches.   Female breeding hamsters require much larger areas for housing them and their litter just before weaning.  Twelve-hour light cycles are preferred, as hamsters are more active during the night.

Bedding must be clean, nontoxic, absorbent, relatively dust-free, and easily acquired.  Shredded paper or tissue and processed corncob are all appropriate.  Make sure that wood shavings and ground corncobs are free from mold, mildew, or other contamination before using.  Do not use cedar chips or chlorophyll-scented shavings. These materials have been associated with respiratory and liver disease in rodents.  Provide at least 2 inches of bedding in the cage to allow for normal burrowing behavior.  Cotton and shredded tissue paper make excellent nesting materials.

It is best to house pet hamsters singly.   Mature female hamsters tend to be very aggressive toward on another and should never be housed together.  Additionally females are larger and more aggressive than males.  Thus, males usually need to be separated immediately after breeding.   Males may also fight when housed together, but they tend to be less aggressive than females.

Your pet hamster's cage and accessories should be thoroughly cleaned at least once a week.  When newborns are present, however, wait until they are at least 2 weeks old to clean the cage.  You may want to clean more frequently than once a week depending on the number of animals in the cage, the type of bedding material used, and the cage design and size.  It is best to clean a cage with hot water and a nontoxic disinfectant or detergent.  Be sure to thoroughly rinse away all traces of the disinfectant or detergent.  Water bottles and food dishes should be cleaned and disinfected daily.

Breeding

Sex determination is fairly obvious in hamsters.  Mature male hamsters possess large, prominent testicles just beneath their tails.  Often the testicles' size is alarming when first noticed or may be mistaken for tumors.  In addition, the genitourinary to anal separation is much wider in males than in females, making it possible to differentiate genders of young hamsters.

Female hamsters can be bred at 6 to 10 weeks of age.  Male hamsters can be bred at 10 to 14 weeks of age.  As the female comes into heat, she will begin assuming a breeding stance with her back swayed and body stretched out.  When petted over her back she will remain motionless and sway her back even further.  A thin mucus will be noticed coming from her vulva.  For breeding, place the male into the female's cage about 1 hour before dark.  Closely observe the pair for mating activity or fighting.  Females can be very aggressive toward males and can cause serious injuries.  at the first sign of aggression, separate the animals, then try again the next night.  Remove the male shortly after a successful mating has taken place.  It is recommended that the cage be cleaned 2 weeks following breeding so it is clean when the babies arrive.

Length of pregnancy is short in hamsters, lasting only 15 to 16 days.  Just before delivery, the expectant mother will become restless and may discharge a small amount of blood from her vulva.  Do not handle or disturb the expectant mother at this time.

Litter size ranges from five to ten pups.   However, larger litters are not uncommon.  The pups are born hairless with their eyes and ears closed.  They already have their front teeth, known as incisors. 

Provide ample nesting and bedding for the new mother and babies.  Plenty of fresh food and water should be available before the babies are born. Do not disturb the mother and young for any reasons during the first week after birth.  When a mother hamster feels threatened, it is common for her to kill and cannibalize her young.  in other instances, she may stuff the young into her cheek ouches and frantically carry them around the cage, looking for a safe place to establish a nest.  Occasionally, pups will suffocate as a result of this activity, especially if the disturbance is prolonged.

Young hamsters usually begin eating solid food at 7 to 10 days of age but are not weaned until 21 to 25 days.  Provide regular food on the cage floor for the young and include soaked, softened pellets for them as well.   Make sure that the water bottle is low enough for the weanlings to use and that they are strong enough to use it.  If they are not strong enough, provide an alternate water source for them.

Hamster Diseases and Syndromes

Wet Tail (Proliferative Ileitis).
The most commonly encountered bacterial infection in hamsters is "wet tail".   The precise cause of the disease is not fully understood, but underlying infections with Campylobacter bacteria have been reported.  Other pre-disposing factors such as improper diet, sudden dietary changes, overcrowding, and other stresses are involved in causing the disease.

Wet tail commonly affects weanling hamsters between the ages of 3 to 6 weeks, but hamsters of all ages are susceptible.  This is a common disease encountered in recently acquired pets.  The long haired Teddy Bear hamster seems to be more vulnerable than other varieties of hamsters.

This disease often strikes with very little warning.  Death may result within 1 to 7 days after the onset of watery diarrhea.   Other signs of disease include matting of the fur around the tail, unkempt haircoat, hunched stance, loss of appetite, dehydration, emaciation, and irritability.    Blood from the rectum and rectal prolapse may be noticed in some advanced cases.  If you hamster is exhibiting any of these signs, contact your veterinarian at once.  Specific antibiotics and supportive care can be attempted to treat wet tail, but unfortunately, death results in just a few days in most cases.

Hair Loss (Alopecia)
Hair loss can occur for a number of reasons in hamsters and can be due to both disease and non-disease conditions.  Continual rubbing on feeders or sides of the cage and barbering (hair chewing by cage mates) are examples of non-disease causes of alopecia.   Infestation with demodectic mites is one of the most common infectious causes of patch alopecia. and crusty skin an hamsters.  Other conditions that lead to hair loss include adrenal tumors, thyroid deficiency, and chronic kidney disease.  Some of these conditions may be manageable while others are not.

Old Age Diseases (Geriatric Conditions)

Hamsters tend to have relatively short lifespans when compared to other species.  The average life expectancy of a hamster is between 2 and 3 years.  For this reason, aging disorders are not uncommon in these animals.  Two of the most common geriatric diseases of hamsters are amyloidosis (protein deposition in various organs) and cardiac thrombosis (blood clots in the heart).  Treatment of these conditions involves managing clinical signs since cures are not possible.  Most geriatric diseases are not curable and often result in the hamster's death.

Amyloidosis is a condition whereby protein produced by the body are deposited in various organs, primarily the liver and kidneys.   Kidney and liver failure often occur as a result of these protein deposits.   Many other organs are also affected, and the changes are irreversible.  signs of this condition include swollen abdomen, urinary problems, dehydration, poor appetite, and rough haircoat.  Supportive care is the only treatment since this condition is eventually terminal.

Blood clots within the heart typically occur in the left side of the heart in older hamsters.  Many factors are involved in the formation of these clots including clotting disorders, heart failure, and circulation bacterial infection.

Many other geriatric diseases occur in hamsters over the age of 1 year.  Liver and kidney diseases are not uncommon in middle-aged and older hamsters.  Other conditions commonly encountered are stomach ulcers, tumors, and dental diseases.