It's not uncommon for me to see a picture posted online of a skinny pig in mildly distressed condition and then hear the piggy passed away within one or two days, despite everything the owner (and often also their vet) tried. Raising hundreds of skinny pigs over the past decade, I feel like I've learned a lot. And in the beginning, like everyone, I learned a lot of stuff the hard way. By seeing guinea pigs get a little sick, deteriorate and then pass away. They might be under vet supervision for a week, or might be gone overnight. There are a lot of things that can cause a skinny pig to become ill and crash, but I can't stress enough:
Let me try to explain. A guinea pig's natural body temperature is 103-104F (39.4-40C). Skinny pigs have little or no fur to insulate them and help keep them warm. They also often do not have as much body fat as furry guinea pigs. This is fine for an average healthy skinny pig living in a room that's about 70F (21C). They're eating a ton of food and easily able to keep their body at ~33F higher than the room temperature.
What happens when they get stressed or get a digestive upset or some other illness? Their body starts putting energy into healing. After all, if they don't work at recovering they will just continue to get worse. But their normal consumption of food was just keeping them fit and healthy and keeping their body temperature up. When some of those calories get diverted towards healing, they're no longer available for keeping their body as warm. So the guinea pig starts to get colder and move slower and now is probably taking in less calories because they don't feel well. They can spiral down, even dying, pretty quickly.
How does increasing the ambient temperature help? If you can make it so they don't have to work as hard to keep their body at 103-104F then they can spend more calories healing. Additionally, if they get too cold, their internal organs will begin to shut down and that's not always something they can recover from, even if you provide them with enough warmth afterward. If your hairless guinea pig's health is at all in question, I recommend heat therapy as the very first thing you do, even before you call your vet. Which means you have to have the means to do this on hand before something happens.
There are many ways to do it, and they are NOT equal. In the order of my own personal experience and success I rank them as:
1) Brooder lamp
This is a red heat lamp sold for baby chickens or other baby birds. These lamps are extremely hot and I ONLY recommend you use them if you are already familiar with them and feel safe and confident you can use them without burning your pets or burning your house down. They have been known to cause house fires if they get knocked over or if they are too close to a flammable material and light it on fire. If you use a brooder lamp for your sick guinea pig I recommend starting with it at least 2.5 feet away from your guinea pigs. Set up the lamp so that it points at one corner of the cage and so your guinea pig can choose to be under the warm light or in a cooler part of the cage. Personally, I get my warm corner up to about 85F (29.4C).
2) Small space heater
By this I mean the kind of small heaters people might keep under their desk in the winter. They can have a metal coil, but the very safest kind are oil-filled and literally cannot start a fire. This space heater can be positioned near one corner of the cage to try to get the temperature at the corner up closer to 85-90F (29.4-32.2C). Once again, you want one corner or side of the cage to be warmer and the other end to be more like normal.
3) Ceramic heat lamp
These are sold for reptile owners and are a safe alternative to the old style heat lamp (like the red brood lamp) that were known to cause house fires. The ceramic bulbs don't put out as much heat as the brood lamp and need to be placed closer to the cage/guinea pigs but they do still provide a good heat. As above, you want one corner hotter than the other. All these ideas are trying to accomplish the same thing.
4) Chew-proof heating pad
These are often sold for cats, dogs or rabbits who are living outside in cold weather. Their electrical cord is inside a flexible metal tube designed to withstand mild chewing. You can put this whole thing directly into your guinea pig's cage. I was very excited when I first learned about these and bought a couple of them. Over time I've stopped using them entirely though. If you just put it into the cage it warms up their belly but not their whole self. I did not have good experiences using these to help a guinea pig recover. If this is all you have available, your best bet will be to put it underneath a house, hut, pigloo or other similar place a guinea pig will hide in and huddle in. Put fleece over the pad so your pet is not directly in contact with it and then cover the hut, house or whatever it is, with one or more layers of fleece to try to help trap warm air inside that space.
5) Regular human-use heating pad
These are really scraping the bottom of the barrel for use with sick skinny pigs because they are absolutely NOT safe to leave inside the guinea pig cage and when trying to set them up outside the cage it's very difficult to get the heat to transfer through the bottom of the cage, through the bedding and all the way up to where your guinea pig needs it. It can also be hard to buy one that doesn't have an automatic shut-off after a certain period of time. While healing, your skinny pig needs access to increased heat constantly, no interruptions. Human-intended heating pads can be used while your guinea pig is supervised, usually while being held and comforted by you or another grown up while a better heat solution is put into place.
6) Nothing
I don't even want to add this, but I often hear from people who are trying to keep their guinea pig warm by taking their normal house and covering it in fleece. This is not an adequate way to provide heat for your guinea pig. It's not actually providing heat but relying on your guinea pig's own body heat (and I've explained above why that's failing) to heat the air in the house. Yes, the fleece will help trap the heat but if your skinny pig is sick, it needs you to provide additional heat support. This is your obligation as the pet-owner who took on the responsibility of your pet.
Nothing above should replace medical treatment by an experienced guinea pig veterinarian. This is all what I recommend to stabilize your guinea pig's condition while you set up a vet appointment and what you should practice until your guinea pig has recovered from his or her illness. You will know when you can remove the added heat. The more time your guinea pig spends in the heated area of the cage, the more he or she *needs* that heat. Once he or she spends little or no time there, that's when they don't need it anymore. I always practice heat therapy in tandem with whatever my vet prescribes.
Warmth will help your guinea pig recover but you do need to be careful that you don't provide an unsafe level of heat. Signs of heat distress, heat exhaustion, heat stroke, or burns include (but are not limited to): +Laying really flat, like a pancake, while wide awake +Fast and noticeable breathing +Skin feeling clammy or sticky (skinny pigs, not Baldwins who may naturally feel like this) +Skin turning red or developing a spot or circle of red, discolored or altered skin, usually on the back, or an area closest to the heat lamp +Edges of the ears are dry or appear damaged If any of these signs are noticed, you should remove and re-evaluate your heat immediately to make sure it's not causing distress or injury to your pets.