If, and only if, all health related issues are ruled out and the cause for thinning fur cannot be determined, there are steps you can take to help resolve a thinning or balding coat.
There are 3 remedies that can help bring back a coat. Please keep in mind that the first 2 rarely work on their own. If used, they are most effective when used in conjunction with the third grouping of treatment.
1.Melatonin. This is safe for dogs (in moderate quantities) and is part of an encompassing plan to prompt fur to grow back in. This can make a dog feel sleepy or drowsy, so you'll want to discuss this with your vet first. Dosing is 1 mg per day for 4 to 8 pound Chihuahuas. Melatonin manufactured for human consumption is often of a higher quality than that made for canines and for this reason, is recommended.
Omega 3, 6, 9.
This supplement plays a role in maintaining and restoring healthy skin and coat.
Restorative coat/bath products.
The DerMagic line of products works very well if you are willing to put in the effort. You will want to use the rescue lotion twice daily
for the 1st week; this is massaged into any thinning or balding spots for at least 5 minutes. Then, starting at week #2 and moving forward until the coat is back to normal, massage once per day.
Along with this, bath your Chihuahua every two weeks, using both DerMagic shampoo and conditioner. Do not blow dry. Use a towel to blot and allow to air dry.
You should see improvement after 4 weeks and many Chihuahuas have a full coat after 2 months. If this does indeed work for your Chi, you may need to routinely use these products to keep the fur from falling out again.