Top-Line Results from thePhase 3 INVIGORATE-2 Trial in Allergic Conjunctivitis DATA RELEASE June 15, 2023 Nasdaq: ALDX © Aldeyra Therapeutics, Inc. 2023

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The Phase 3 INVIGORATE-2 Trial of Reproxalap in Allergic Conjunctivitis Achieved All Primary and Secondary Endpoints Statistical significance was achieved for: The primary endpoint of reduction in ocular itching at all prespecified timepoints (P<0.0001) The key secondary endpoint of reduction in ocular redness (P=0.004) All secondary endpoints (ocular tearing [P<0.0001] and total ocular severity score [P<0.0001]) †Ann Allergy Asthma Immunol, 108(3): 163-6, 2012. Topical ocular reproxalap is an investigational drug candidate that has been studied in more than 2,400 patients with no observed safety concerns; mild and transient instillation site irritation is the most commonly reported adverse event in clinical trials. The results are consistent with other allergic conjunctivitis clinical trials of reproxalap: the Phase 3 INVIGORATE Trial, the Phase 3 ALLEVIATE Trial, and a Phase 2 allergen chamber trial. The observed activity of reproxalap in allergic conjunctivitis may also benefit patients with dry eye disease, approximately half of whom suffer from ocular allergy.†

The Allergen Chamber:A Demanding Real-World Drug Assessment in Allergic Conjunctivitis Slide source: Cliantha Research The allergen chamber Enables a controlled, environmental allergen exposure that mimics real-world exposure to airborne allergens Allows for detailed assessment of prophylaxis and treatment with unparalleled standardization To our knowledge, no other late-stage investigational allergic conjunctivitis drug has been rigorously tested in an allergen chamber. Patients are exposed to moderate to high levels of ragweed pollen continuously for approximately 3.5 hrs Drug or vehicle is administered prior to allergen exposure and at 90 minutes, when peak symptoms typically occur Patient-reported ocular itching and tearing scores, and investigator-assessed ocular redness scores, are obtained approximately every 10 min 4

The Phase 3 INVIGORATE-2 Allergic Conjunctivitis Trial Design Design Randomized, two-way crossover, vehicle-controlled, double-masked allergen chamber challenge design with 0.25% topical ocular reproxalap Chamber Exposure & Dosing Schedule 3.5 hours continuous allergen exposure First dose just before chamber entry Second dose 90 minutes after entry (peak allergy symptoms) Inclusion/Exclusion Criteria History of moderate to severe allergic conjunctivitis to ragweed pollen Itching score of ≥2.5 and redness score ≥2 in baseline chamber assessment ClinicalTrials.gov Identifier: NCT05234554 Primary Endpoint Statistical significance in patient-reported ocular itching (0-4 scale) at a majority of 11 timepoints between 110 and 210 minutes Key Secondary Endpoint Change from baseline in investigator-assessed ocular redness (0-4 scale) over the duration of the allergen chamber Secondary Endpoints Patient-reported ocular tearing score (0-3 scale) Total ocular severity score (11-point composite of itching, redness & tearing)

The INVIGORATE-2 Trial Achieved All Primary and Secondary Endpoints P values derived from mixed effect model of repeated measures analysis. Topical ocular reproxalap is an investigational drug candidate that has been studied in more than 2,400 patients with no observed safety concerns; mild and transient instillation site irritation is the most commonly reported adverse event in clinical trials. Primary Endpoint:ACHIEVED Key Secondary Endpoint: ACHIEVED Both Secondary Endpoints: ACHIEVED NO Observed Safety or Tolerability Concerns Statistically significant improvement vs. vehicle (P<0.0001) over all 11 prespecified timepoints of patient-reported ocular itching score from 110-210 minutes in the allergen chamber Statistically significant improvement vs. vehicle (P=0.004) on key secondary endpoint of investigator-assessed ocular redness over the duration of the allergen chamber Statistically significant improvement vs. vehicle on secondary endpoints of patient-reported ocular tearing and total ocular severity score achieved (P<0.0001 for both endpoints) over the duration of the allergen chamber 131 subjects enrolled, 130 of whom completed both treatments; no discontinuations due to adverse events

Reproxalap Achieved Primary Endpoint of Reduction inOcular Itching in the INVIGORATE-2 Trial Primary endpoint of statistical significance for majority of timepoints achieved over prespecified time frame of 110-210 minutes after allergen chamber entry in change from baseline in patient-reported ocular itching All timepoints within 110-210 minutes statistically significant in favor of reproxalap (P<0.0001 for each timepoint) Prophylactic and treatment effects of reproxalap demonstrated P values derived from mixed effect model of repeated measures analysis. Topical ocular reproxalap is an investigational drug candidate that has been studied in more than 2,400 patients with no observed safety concerns; mild and transient instillation site irritation is the most commonly reported adverse event in clinical trials. KEY RESULTS

Reproxalap Achieved Key Secondary Endpoint of Reduction in Ocular Redness in the INVIGORATE-2 Trial Key secondary endpoint of statistical significance in change from baseline in investigator-assessed ocular redness over the entire chamber achieved (P=0.004) Prophylactic and treatment effects of reproxalap demonstrated KEY RESULTS P values derived from mixed effect model of repeated measures analysis. Topical ocular reproxalap is an investigational drug candidate that has been studied in more than 2,400 patients with no observed safety concerns; mild and transient instillation site irritation is the most commonly reported adverse event in clinical trials.

Reproxalap Achieved Secondary Endpoint of Reduction inOcular Tearing in the INVIGORATE-2 Trial Secondary endpoint of statistical significance in change from baseline in patient-reported ocular tearing score over the entire allergen chamber achieved (P<0.0001) Prophylactic and treatment effects of reproxalap demonstrated KEY RESULTS P values derived from mixed effect model of repeated measures analysis. Topical ocular reproxalap is an investigational drug candidate that has been studied in more than 2,400 patients with no observed safety concerns; mild and transient instillation site irritation is the most commonly reported adverse event in clinical trials.

Reproxalap Achieved Secondary Endpoint of Reduction inTotal Ocular Severity Score in the INVIGORATE-2 Trial Secondary endpoint of statistical significance in total ocular severity score, a composite of patient-reported ocular itching and tearing scores and investigator-assessed ocular redness score over the entire allergen chamber, achieved (P<0.0001) Prophylactic and treatment effects of reproxalap demonstrated KEY RESULTS P values derived from mixed effect model of repeated measures analysis. Topical ocular reproxalap is an investigational drug candidate that has been studied in more than 2,400 patients with no observed safety concerns; mild and transient instillation site irritation is the most commonly reported adverse event in clinical trials.

Reproxalap Was Generally Well Tolerated and No Safety Concerns Were Observed in the INVIGORATE-2 Trial No observed safety or tolerability concerns No discontinuations due to adverse events Consistent with other topically administered drugs, most common treatment-emergent adverse events related to transient instillation site irritation No observed clinically significant findings on safety assessments, including: visual acuity intraocular pressure slit lamp biomicroscopy dilated fundoscopy TOPICAL OCULAR REPROXALAP administered to more than Topical ocular reproxalap is an investigational drug candidate that has been studied in more than 2,400 patients with no observed safety concerns; mild and transient instillation site irritation is the most commonly reported adverse event in clinical trials. 2,400 patients 21 clinical trials across

Reproxalap Demonstrated Consistent Improvement in Ocular Itching Symptoms Across Late-Stage Allergic Conjunctivitis Clinical Trials Consistent statistically significant symptomatic activity of reproxalap over vehicle in patients with allergic conjunctivitis demonstrated across Phase 2 and Phase 3 allergen chamber trials Large effect sizes suggest clinically meaningful difference between reproxalap and vehicle in reduction of patient-reported ocular itching KEY RESULTS Topical ocular reproxalap is an investigational drug that has been studied in over 2,400 patients with no safety concerns reported; mild instillation site discomfort is the most commonly reported adverse event in clinical trials. Effect size is change from baseline divided by baseline standard deviation. CI = confidence interval.

Reproxalap Demonstrated Consistent Reduction of Ocular Redness Across Two Distinct Crossover Chamber Challenge Models of Ocular Surface Disease Consistent statistically significant activity of reproxalap over vehicle in reduction of ocular redness demonstrated across Phase 2 and Phase 3 chamber trials in allergic conjunctivitis and dry eye disease Overall effect size exceeds clinically relevant threshold of 0.5 for ocular redness between reproxalap and vehicle KEY RESULTS Topical ocular reproxalap is an investigational drug that has been studied in over 2,400 patients with no safety concerns reported; mild instillation site discomfort is the most commonly reported adverse event in clinical trials. Effect size is change from baseline divided by baseline standard deviation. CI = confidence interval.

Allergic Conjunctivitis and Dry Eye Disease Are Interrelated Inflammatory Ocular Surface Diseases Slide sources: *Concepts adapted from “The Whipsaw of Allergic Dry Eye” by Mark B. Abelson, MD and Lauren Lilyestrom in REVIEW of Ophthalmology; October 2008; and Ann Allergy Asthma Immunol, 108(3): 163-6, 2012. POLLUTANTS “The clear interaction of allergy, dry eye and environmental irritants makes untangling their etiology in prevalence studies difficult.”* Dry Eye Disease Allergic Conjunctivitis Allergic response can compromise tear film Dry eye inflammation can enhance allergic response Dry, polluted environments exacerbate both conditions POLLENS Allergens Irritating Air PARCHED ENVIRONMENTS

Aldeyra Has Submitted What is Believed to be the Most Comprehensive Dry Eye Disease NDA, which Includes Symptoms and Multiple Signs† †The NDA submission includes a combination of primary, secondary, multiplicity-adjusted, and nominal P-value endpoints. ‡Adequate and well-controlled Phase 2 or Phase 3 clinical trials can be submitted as pivotal. NDA = New Drug Application, SEM = standard error of the mean. Topical ocular reproxalap is an investigational drug candidate that has been studied in more than 2,300 patients with no observed safety concerns; mild and transient instillation site irritation is the most commonly reported adverse event in clinical trials. Phase 2 Dry Eye Chamber Trial ‡ Phase 3 RENEW–Part 1 Formulation Phase 2‡ P=0.03 Schirmer Test Phase 3 TRANQUILITY-2 Trial Ocular Redness Ocular Dryness Symptom Score ≥10 mm Schirmer Test Responder Analysis P=0.0001 Phase 3 TRANQUILITY-2 Trial P=0.0004 Dryness Symptom Score Change from Baseline ± SEM Dryness Symptom Score Change from Baseline ± SEM Crossover Trial Crossover Trial Change from Baseline Change from Baseline Odds ratio 2.625 P value versus vehicle <0.0001 Raw Score Change from Baseline Odds ratio 1.551 P value versus vehicle 0.0361 P=0.016 P=0.0005 P=0.0004

†Regulatory review timelines are flexible and subject to change based on the regulator's workload and other potential review issues. ‡The timing of ongoing clinical trials depends, in part, on the availability of clinical research facilities and staffing, and the ability to recruit patients. *Investigator sponsored. Primary Vitreoretinal LymphomaPDUFA date of June 21, 2023† Proliferative VitreoretinopathyType C meeting with FDA to discuss completion of clinical development planned for H2 2023 Retinitis PigmentosaPhase 2 clinical trial top-line results expected in Q2 2023‡ Dry Eye Disease PDUFA date of November 23, 2023† Atopic Dermatitis (Part 1), Chronic Cough, Idiopathic Nephrotic Syndrome (Part 1), and Sjögren-Larsson Syndrome*Phase 2 clinical trial top-line results expected in 2023‡ Moderate Alcohol-Associated HepatitisInitiation of Phase 2 clinical trial expected in H2 2023‡ Upcoming Planned Clinical Milestones ADX-2191 Reproxalap ADX-629