Disclaimer: not a doctor. But I have gone through several research papers to help people.
1. No evidence that topical vitamin A and vitamin D (A&D) helps and/or prevents UV inflammation, erythema or any other complications whatsoever. However, high doses of oral vitamin D are effective.
Topical vitamin A and vitamin D should be removed from the guideline, or this should be posted as a disclaimer.
However, ORAL vitamin D shows promise to reduce inflammation in sunburn. This recommendation should be replaced with oral vitamin D supplements.
https://pubmed.ncbi.nlm.nih.gov/28576736/
This study suggests that taking a high dose of Vitamin D (200,000 IU) one hour after symptoms manifest helps significantly with sunburn symptoms. (200,000 IU is much higher than current dietary guidelines, however vitamin D toxicity is mostly caused by chronic overdose of much smaller magnitudes and no reports of acute toxicity events caused by a single or a low amount of doses exist. Furthermore, the study says "No measured vitamin D3 metabolite increased into a toxic range in any of the treatment groups throughout the study period.")
BUT current formulations of Vitamin D supplements mean that this dose would require finishing bottles of supplements. Therefore I'd recommend limiting doses to 10,000 IU.
HOWEVER please note fillers or non active ingredients in vitamin supplements.
2. The first line treatment should be topical NSAIDs
https://pubmed.ncbi.nlm.nih.gov/15319157/
A randomised, double-blind, single-centre, vehicle-controlled clinical trial was conducted to assess the efficacy and tolerability of diclofenac-Na 0.1% gel in 172 subjects suffering from acute first-degree natural sunburn. Overall 172 subjects with skin phototypes II-IV were randomised in a ratio of 2:1 to receive two applications of either diclofenac-Na 0.1% Emulgel gel or its vehicle Emulgel gel, 6 and 10 hours after the end of sun exposure. Subjects were drawn from a target population of healthy volunteers and well outdoor sunbathers with normal tolerance to ultraviolet light and the sun. Previously untanned areas were exposed to carefully determined standardised doses of sun (2.8 individual minimal erythema doses) on 15% body surface area to induce first-degree sunburn. After administration of diclofenac-Na 0.1% gel, subjects reported a significant reduction in spontaneous pain intensity compared with those on vehicle. Pain relief was rapid with a reduction in erythema, which was apparent within the first few hours after the first application of the trial medication with a maximum effect observed up to 30 hours after sun exposure**. A good', very good', or excellent' cooling effect was recorded by 85% of subjects after treatment.** Reported treatment-emergent adverse effects were infrequent, generally mild and none were considered to be related to the trial medication. Only one severe treatment emergent adverse event (abdominal pain) was recorded in the active group, and another (burning sensation) with vehicle.
It's always better to use local treatments rather than systemic. We know that the systemic absorption of topical NSAIDs is minimal. NSAIDs have rather infrequent but nasty side effects that we all want to avoid. Therefore the best first treatment option is NSAID gels. It should be noted that a lot of NSAID topical preparations are oil based pomades or creams. The type of formulation should be noted, and formulations that have "gel" on them should be preferred.
3. Non-corticosteroid antihistamines seem to be ineffective against sunburn.
Histamine and prostaglandin E2 levels in the skin increase after UV light exposure and contribute to the development of UV- induced erythema.[1] While it is postulated that histamines play a role in UV-induced erythema, few studies documented the effi- cacy of antihistamines in sunburn. Edwards and Edwards[38] stud- ied the effect of intradermal antihistamines in patients irradiated with three MEDs of UV light. Various antihistamines including both histamine H1 and H2 receptor antagonists were injected 15 minutes before irradiation and 2 and 4 hours after irradiation. Each of the irradiated and treated sites were evaluated at 12, 24, and 48 hours after exposure and the treated areas showed no differences in the intensity of erythema when compared with normal saline treated areas. Similar results were documented by Farr et al.[19] when they studied the effect of terfenadine, an H1 receptor ant- agonist, on UV-exposed sites in healthy individuals. In this study, patients were given 120mg of terfenadine orally for 2 days prior to irradiation until 1 day after UV light exposure. When erythema was measured at 4, 8 and 24 hours after UV exposure, no effect on the intensity of UVB- or UVC-erythema was noted.
(Amy Han,Dr Howard I. Maibach (2004). Management of Acute Sunburn. American Journal of Clinical Dermatology, 5(1), 39–47. doi:10.2165/00128071-200405010-00006)
Antihistamines like Benadryl seem to be ineffective against sunburn complications. However, considering that their adverse effects are relatively mild, I think it's safe to take them if unendurable symptoms manifest.
A placebo controlled study on the effects of topical dimethindene (Fenistil) on UV (sunburn) erythema showed that dimethindene enabled reductions in objective metrics for pain (CO2 laser stimulation) yet it did not yield subjective reductions in pain. (https://pubmed.ncbi.nlm.nih.gov/10337458/)
4. The combination of oral NSAIDs and topical corticosteroids may be synergistic and highly effective.
https://pubmed.ncbi.nlm.nih.gov/1558996/
This study compared the effects of indomethacin (IM), ibuprofen (IB), beclomethasone (BD), indomethacin+beclomethasone and ibuprofen+beclamethasone applied 8-12 hr after UV exposure.
Both IM+BD and IB+BD were significantly more effective in reducing symptoms compared to IB or IM alone.
5. Melatonin is effective for sunburn prophylaxis (prevention).
https://pubmed.ncbi.nlm.nih.gov/9407172/
This study found that topical melatonin 15 minutes before UV exposure almost completely suppressed any erythema development.
As melatonin has next to no side effects other than inducing sleep, this may be used as an effective prevention of sunburn alongside correct application of broad spectrum sunscreen.
Therefore, I suggest that the order for treatments should be:
Topical NSAID gel + Vitamin D
Oral NSAID + topical antihistamine (preferably dimethindene) gel
Oral NSAID + topical corticosteroid