Hi  – oral lichen planus is a a localized autoimmune disease and there is much disagreement in the conventional medical community about root cause. This is a common situation in disorders where we see an overlap in inflammatory, infectious, and/or autoimmune causes. It is just a matter of the particular progression and manifestation in each individual person. Conventional medicine often looks unrealistically for a single, common trigger, but the immune system is a complex, uniquely-programmed control system in every human body.

It is often cited that a bacterial or fungal infection coincides with lichen planus/lichen sclerosis. This can be a direct factor on the skin itself, in the oral cavity, or it can be internal, simmering infections. I would recommend doing a comprehensive stool analysis (I discuss this in my Gut Health Masterclass course) and addressing any microbial imbalances uncovered.

Consuming fermented foods like sauerkraut, coconut kefir (because I believe dairy should be eliminated in this case), kimchi, etc, is a great way of introducing beneficial probiotics both orally and in the gut if you aren’t histamine intolerant. I share many fermented food recipes in Discounts & Resources. Start slow with 1 tsp and increase gradually to at least 1/4 cup per day. There is recent research on the oral microbiome and oral lichen planus.

Because of its relative prevalence in women 40 years or older, it is postulated that hormone imbalance plays a role, perhaps low progesterone, low estrogen, low testosterone, or a mix of these.  There is evidence that low 5 alpha reductase enzyme activity may play a role. You may want to consider urinary hormone metabolite testing to uncover any hormonal imbalances that might be at play. I like the DUTCH test for all of these markers. This testing will also provide a look at cortisol levels and curve. Low cortisol is also often involved in autoimmune activation.
Also check thyroid levels with a full thyroid panel: TSH, Free T4, Free T3, Reverse T3 and both TPO and thyroglobulin antibodies. Subclinical hypothyroidism is often involved in adrenal dysfunction and is believed to play a role in the hormone imbalance often at the root of lichen sclerosis/planus activation.

As I mentioned in your introduction post, autoimmunity (regardless of the diagnosis) will always have these 3 factors at play: leaky gut/gut dysfunction, immune dysregulation, and trigger(s) (which varies from person to person). Triggers can be infectious (viral, microbial, fungal, parasitic), emotional/physical traumas, food sensitivities, mold, heavy metals, chemical toxins, etc.

Because it helps to increase weak estrogens safely and has strong anti-inflammatory properties too, I recommend supplementing with two heaping tbsp ground flaxseed daily (but don’t do this until after the hormone samples have been collected if you’re doing so, to ensure an accurate baseline).
Food sensitivities are often involved with autoimmune activation or chronic inflammatory symptoms. I would definitely recommend elimination of dairy foods and all added sugars/sweeteners and grains (which will get rid of the inflammatory trigger of gluten but also the common exacerbating effect of grains on intestinal microbial imbalance).
Lastly, consider checking basic nutritional sufficiency for vitamins and minerals that strengthen the immune system, in particular vitamin D, vitamin A, and RBC zinc.

In terms of disease management (not root cause) solutions, here are some additional areas to consider:
• Homeopathic “Ignatia” as a treatment
• Consumption of purslane
• Systemic selenium supplementation (this can also be tested in blood)
• Antioxidants astaxanthin and quercetin
• Probiotics
• Topical chamomile gel for management
• Low level laser therapy 

I hope the above gives you a clearer direction and some areas to explore and take action. If you have the financial means to get a comprehensive stool test and some basic blood tests, I would start there.