It's pretty well known that there are many Hair Envy Review autoimmune conditions that cause hair loss including alopecia areata, lupus, and Hashimoto thyroiditis. Many doctors are reluctant to place psoriasis in this category, but I personally think that you can make this argument as the timing between the two will often suggest a connection. The treatment for these conditions vary. But in terms of hair loss, there is a European study that has shown promise using and rotating specific essential oils rubbed into the scalp.
Other Theories On Hair Loss, Hair Thinning, Or Shedding Along With Psoriasis: Many doctors will tell you that when this condition occurs on the scalp, the plaque and scales can choke out the hair follicles and keep healthy hair from growing (only while there is a flare in place.) Often, this doesn't not occur over the entire scalp. There will more often be patches that you can clearly see being affected and that is where you'll see the hair being compromised or thinning. (This process is pretty hard to miss and is pretty obvious upon close inspection.) However, typically when the area heals, the hair will become normal again.
The other possibility is that a flare has placed stress upon the body. The body in turn will often shut down some functions to conserve. One of these function is the hair growth cycle and what you will get as the result is a condition called TE (or telogen effluvium.) This happens when a large number of hairs move from the growth cycle to the rest cycle.