In an effort to help with that, a group of fourth-year vet students from Glasgow University has set up a clinic service to provide free vaccinations, micro-chipping, clothing, bedding and more.
"My pal bought him for me," says Michael of his three-year-old Staffordshire Bull Terrier, Giro. The two are sitting in the doorway of a Glasgow bank, sheltering from the rain.
He was named because Michael got him on what he calls a giro day - the day he receives his benefits money.
"My pal asked me what I wanted for Christmas and I said a wee bit of company.
"I know it sounds stupid," he adds with a laugh, "but I just wanted somebody to talk to and the puppy does it for me.
"He just sits there with you and he's dead loyal. I just love him to bits."
Michael has been on the streets on and off since 2005. Sometimes he is able to stay with friends but other times he and Giro end up outdoors. For nights like that they have a routine.
"You just get plenty of cardboard on the ground and a couple of sheets of cardboard over the top of you - a door mat, anything like that, just to put a bit of weight on you and then the dog cuddles up next to me and the two of us are warm as toast."
Michael and Giro have a regular spot where they sit. Passers-by who stop to put money in the cup, often take a moment to give the dog a pat too. Others bring or buy food for Giro.
"He doesn't suffer," says Michael.
"He's better than me, put it that way. He's guaranteed a meal. I'm not."
Giro is also wearing a coat against the winter chill which he got from the Trusty Paws clinic.
It was set up this year by Glasgow University vet students.
"We provide basic preventative health care," says 22 year-old Ruby Shorrock, who came up with idea after seeing a similar scheme in England.
They launched in March and over the summer collected supplies and public donations. In October they held their first clinic.
They provide things such as vaccinations, flea and worming treatment, micro chips and general clinical exams, as well as other things including food and collars to dog owners who are homeless.
"They really care for their dogs even more than they care for themselves," says Ms Shorrock.
"Often the dogs get fed before their owners get fed. So just seeing that dedication and passion from someone who's in that predicament is inspiring."
"The aim is to help these people off the streets, so if they're not worrying about feeding their dog or getting care for their dog, they can look after themselves."
The clinics have been held at the advice and information hub of the Glasgow Simon Community. The organisation, which aims to combat the causes and effects of homelessness, is partnering in the Trusty Paws project.
It has meant that, as well as the dogs being helped, the people too are in a place where they can get the support they need.
"Homelessness is an extremely isolating, lonely and frightening experience," says Lorraine McGrath, chief executive at the Glasgow Simon Community.
In such a situation a dog can become really important.
She says: "Basically they become the one constant, the one positive relationship in their lives.
"They give a sense of purpose, a sense of meaning to each day. It's someone for them to care for and to have responsibility for."
She says dogs can make finding accommodation more difficult. Their services do allow them, but others are not able to take them.
Her organisation has dealt with people who have refused offers of somewhere to stay because they have not been able to take their dog with them.
Certainly Michael says he would not move into anywhere without Giro.
"He's everything to me. I would die for him. He's a great wee pup. He's my wee pal. I've got to look out for him as well."
The relationship between a homeless person and their dog can be an exceptionally close one but if you are on the streets, looking after your pet can also be challenging.