I've been seeing a number of bald dogs in the consulting room recently, and it made me wonder how common a problem it is - and how many conditions there are that can lead to a dog losing his hair! Baldness (or alopecia, to give it its technical name) isn't generally a disease in its own right - it is almost invariably a symptom of an underlying disease condition. So, when I'm faced with a poor, balding dog in the consult room, my first task is to try and define what the underlying cause is. With a symptom with so many possible causes, what we do to narrow down the possibilities is to work out a differential list - a list of all the possible conditions that can cause baldness - and then eliminate them until we come to the actual cause in this specific case. So, in no particular order, here are the more common causes of hair loss in dogs, along with their other major signs or symptoms: Firstly, those disorders that give a symmetrical pattern of hair loss (i.e. the same pattern of hair loss on both sides of the body): Hypothyroidism Hair loss is symmetrical along the trunk and may also involve the tail, armpits and the belly. The skin isn't inflammed or itchy, but there may be a darkening of colour and dandruff or greasy skin. Caused by production of too little thyroid hormone, other common symptoms include lethargy, weight gain, and sometimes muscular weakness. To diagnose hypothyroidism, your vet will take a blood sample; treatment is simple, with daily tablets containing replacement thyroid hormone. Cushing's Disease Once again, hair loss is symmetrical, and there may be hard lumps in or under the skin (calcinosis cutis). Cushing's is caused by too much cortisol (an important natural steroid hormone) being produced by the body. Other symptoms include increased hunger, thirst and urination, development of a pot-belly, muscle weakness, skin thinning and "spots" or "blackheads" developing. To diagnose it, your vet may have to do a series of blood tests to see how your dog's body responds to injections of steroids or other hormones. Tablets to treat Cushing's usually act to reduce production of steroids, although some destroy the adrenal glands that make the excess hormones. Iatrogenic Cushing's Disease This is a form of Cushing's disease caused by long term use of steroid medications (e.g. Prednisolone for severe allergies). The only treatment is to VERY GRADUALLY reduce the steroid dose - but this needs to be done carefully, following advice from your vet, because if you reduce it too far, too fast, it can result in severe withdrawal effects, or even death, due to a lack of cortisol in the body. Sex hormone disorders Excess production of sex hormones (e.g. due to a testicular tumour) or insufficient sex hormones (usually after neutering) can, in rare cases, cause symmetrical hair loss. And now, those diseases where there are patches of hair loss in various sites across the body: Flea Allergic Dermatitis This is probably the commonest cause of all! Dogs with a flea allergy scratch and scratch, and wear the hair away. FAD is usually straightforward to diagnose (very itchy dog plus fleas is something of a giveaway), although in extreme cases, a single flea bite can set it off, which is harder to detect. Prevention is simple - avoid and kill fleas - although it can be hard in severe cases to keep the flea population low enough, and anti-allergy medication may be required. Sarcoptic Mange Mange mites burrow into the skin, creating a very itchy patch covered in little bumps. The dog scratches away at it, wearing the hair away, creating a bald patch. The most common site is on the ear; fortunately, there are some spot-on treatments available from your vet that will kill the mites and stop the itching. Demodectic Mange This is a different variety of mite, and unlike the sarcoptic mite, it doesn't itch at all. Most dogs have a few, and they don't cause any problems, living harmlessly deep inside the hair follicles. However, sometimes they can start to multiply, and the sheer numbers start to result in hair loss. Typically, it is a patchy disease, with hair loss in distinct regions that get bigger over time. Sometimes there is a bit of scale forming, but the mites themselves do not cause itching, although secondary bacterial infection may occur, which can. To diagnose Demodex mites, your vet will have to take a deep skin scrape, usually with a scalpel blade, and then look at it under the microscope. If Demodex mites are found, treatment may involve spot-ons like Promeris Duo, or bathing with Aludex for several months - sadly, it can take a lot of work to get it under control. Primary Pyoderma Bacterial skin infections are common in dogs, and can result in hair loss. The skin is usually reddened and inflamed, and there may be pussy "spots". Often the area is itchy and sore, but occasionally there are cases where the skin looks almost normal but hairless. The vet can diagnose it by taking scrapes and smears from the skin, then looking at them under the microscope. Treatment nay involve antibiotic creams, washes, and sometimes tablets to kill the bacteria. Sometimes a yeast infection can cause the same symptoms; treatment then is usually with anti-fungal washes. Ringworm (Or dermatophytosis) is often diagnosed in practice, generally by using a Woods Lamp, which makes the fungus glow. Its appearance can vary widely, but most looking involves patches of hair loss, sometimes with scales, sometimes itchy (but not always). It's particularly a problem in dogs that are ill with something else, and have reduced immunity. To get a definite diagnosis, hair plucks have to be sent to a lab and cultures, but that can take weeks so vets will often start treatment while waiting for confirmation to come back. Treatment usually involves washes, shampoos and occasionally tablets to kill the fungus, but it can take a long time to completely clear a bad infection. Allergic Reactions (e.g. to a spot-on medicine, or a new floor cleaner, sometimes even to food!). Usually, there is reddening and inflammation of the skin, and itching, before the hair comes out, but occasionally hair loss is noticed first. There are other causes (e.g. genetic disorders, immune diseases like pemphigus) but they are generally far less common. It's important to remember the old adage that "common things are common" before jumping to conclusions. Baldness and hair loss in dogs can be a marker for a serious underlying condition - it's almost never due to simple old age! - but most of these conditions are either curable or at least manageable. And the dogs I saw this week? Well, one was a nice simple skin infection (although it didn't look like it to begin with, the tests were clear and she responded really well to antibiotics). The other one had been on steroids for several years, and the effect over that time had given him Iatrogenic Cushing's. His owners are working to reduce the dose (very, very gradually, as his body has become dependant on the tablets now), and to keep him warm, they've bought him a coat to wear when he goes out in the cold for a walk! If you are worried about bald patches on your dog, talk to your vet or check any other symptoms using our interactive Dog Symptom Guide to help decide how urgent the problem may be.