Pet Care

May Dog Skin Care: Flea Season Begins, Grass Allergies, and Sun Exposure

Based on peer reviewed veterinary research · For educational purposes only · Updated October 2026 · 8 min read

Chlorhexidine Shampoo

Chlorhexidine Shampoo combines chlorhexidine gluconate 2% with ketoconazole 1% to help clear the secondary bacterial and yeast overgrowth that follows flea bites and grass allergy itch.

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Key Takeaways

May is when flea populations accelerate, grass pollen rises, and UV exposure increases, three distinct threats to canine skin in one month.
A single adult female flea can lay up to 40 to 50 eggs per day (Rust & Dryden, 1997), so a few fleas in May can become an infestation by June.
Flea allergy itch concentrates on the lower back, tail base, and hind legs, while grass allergy targets the paws, belly, and face.
Light-skinned and thin-coated dogs are prone to solar dermatitis on the nose and belly, which can progress to precancerous change with repeated exposure.
Scratched, inflamed skin often develops secondary Staphylococcus pyoderma, for which antiseptic shampoo therapy is a guideline-supported option (Hillier et al., 2014).

Products for this topic

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Antiseptic chlorhexidine spray for localized bacterial skin problems, scabs, hot spots and minor wounds.

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Chlorhexidine Shampoo

Medicated chlorhexidine shampoo for widespread bacterial skin problems and recurring pyoderma.

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What Does May Mean for Your Dog's Skin?

May is the month when flea season begins in earnest, grass pollen counts climb, and stronger sunlight starts to affect exposed canine skin. Each of these challenges damages the skin in a different way, and many dogs face more than one at the same time.

Fleas thrive once outdoor temperatures consistently reach the range of about 21 to 30°C (70 to 85°F) with moderate humidity, conditions that much of the Northern Hemisphere reaches in late spring. Because a female Ctenocephalides felis (the cat flea, which is also the most common flea on dogs) can produce 40 to 50 eggs per day (Rust & Dryden, 1997), populations can expand rapidly in yards and homes.

At the same time, grass pollens take over from tree pollens as the main seasonal allergen for many atopic dogs. And longer, sunnier days increase ultraviolet exposure for dogs with pink skin and sparse hair on the nose and belly. May skin care is about stopping fleas early, limiting allergen contact, and protecting vulnerable skin from the sun, before small problems compound into summer infections.

Why Does Flea Season Start in May?

Flea life cycles speed up dramatically as temperature and humidity rise. Under warm conditions, the full cycle from egg to adult can take as little as two to three weeks. Commonly cited estimates suggest that adult fleas on the pet represent only about 5% of the total population, with eggs, larvae, and pupae making up the rest in carpets, bedding, and shaded outdoor soil (Dryden, 2009).

Flea allergy dermatitis (FAD, an allergic reaction to proteins in flea saliva) is one of the most common allergic skin diseases in dogs. In sensitized dogs, even a few bites can trigger days of intense itch. A study of pruritus patterns found that flea-related itch concentrates on the dorsal lumbosacral region (lower back and tail base), which helps distinguish it from environmental allergy (Bruet et al., 2012).

Fleas often go unseen on allergic dogs because constant grooming removes them. Finding flea dirt (dark specks that turn reddish on a damp white paper towel) is often the clue. Our flea allergy dermatitis page and the guide to recovering from severe flea infestation cover this in more depth.

How Do Grass Allergies and Sun Exposure Affect Dogs in May?

Grass pollen allergy is a form of canine atopic dermatitis. Grass pollens such as Timothy, Bermuda, Kentucky bluegrass, and orchard grass peak from late spring into summer. Because dogs walk and lie on grass, allergens contact the paws, belly, armpits, and muzzle directly. International guidelines note that canine atopic dermatitis typically begins between 6 months and 3 years of age (Hensel et al., 2015), so a young dog with a first spring flare is a classic presentation.

Grass awns, the barbed seed heads of grasses such as foxtails, also begin to dry out from late spring and can migrate into paws, ears, and skin (see Herding Dog Skin Hazards).

Solar dermatitis (sun-induced skin inflammation) affects dogs with lightly pigmented skin and thin hair, particularly on the bridge of the nose, belly, and inner thighs. Dogs who sunbathe on their backs are at particular risk. Repeated UV injury can lead to actinic keratosis and, over years, squamous cell carcinoma or hemangiosarcoma in predisposed breeds such as Dalmatians, white Bull Terriers, Whippets, and Pit Bull type dogs (see Sun-Induced Skin Cancer in Dogs).

Signs and Symptoms to Watch For in May

The location of itch or redness is one of the most useful clues for telling May's skin problems apart.

Feature	Flea Allergy Dermatitis	Grass and Pollen Allergy	Sun Damage (Solar Dermatitis)
Main location	Lower back, tail base, hind thighs	Paws, face, ears, armpits, belly	Nose bridge, belly, inner thighs on light skin
Key sign	Intense biting at rump, hair loss, scabs	Paw licking, face rubbing, red belly	Redness, scaling, later crusting or thickening
Trigger	Flea saliva proteins	Grass and late tree pollens	Ultraviolet light
At-risk dogs	Any dog without year-round prevention	Atopic dogs, often under 3 at onset	White, thin-coated, or pink-skinned breeds
Confirmed by	Flea comb, response to flea control	History, exclusion of other causes	Exam, sometimes biopsy

Any of these conditions can be complicated by secondary bacterial infection. Look for small red bumps, pustules, circular crusts with peeling edges (epidermal collarettes), and a worsening odor. These lesions suggest superficial pyoderma, which your veterinarian can confirm with cytology. If you are unsure what you are seeing, the Dog Skin Condition Checker can help you narrow down possibilities before a visit.

How Do Veterinarians Treat May Skin Problems?

Treatment depends on the underlying trigger, and most dogs need a combined plan.

Flea allergy dermatitis. Strict, year-round flea control for every pet in the household is the cornerstone. Modern isoxazoline products kill fleas rapidly, and environmental control (vacuuming, washing bedding) addresses the immature stages. Short courses of anti-itch medication may be used while flea control takes effect.

Grass allergy. Veterinarians use oclacitinib, lokivetmab, or glucocorticoids for flares, and allergen-specific immunotherapy for long-term control (Olivry et al., 2015).

Sun damage. Shade, limiting midday exposure, and veterinary-approved, zinc-free sunscreens or protective clothing reduce UV injury.

Secondary infection. The International Society for Companion Animal Infectious Diseases guidelines recommend topical antiseptic therapy as a primary or adjunctive option for superficial pyoderma, which helps limit unnecessary systemic antibiotic use (Hillier et al., 2014). Chlorhexidine Shampoo contains chlorhexidine gluconate, which binds to and disrupts bacterial cell membranes, together with ketoconazole, which inhibits ergosterol synthesis in yeast. Bathing also physically removes pollen, flea debris, and crusts from the coat. For best effect, lather and leave the shampoo on the skin for 5 to 10 minutes before rinsing, a contact time supported in reviews of topical therapy (Mueller et al., 2012). It is an FDA-registered OTC veterinary drug listed on DailyMed, not a cosmetic shampoo.

Deep infection, fever, or widespread lesions require veterinary assessment and may need systemic therapy. For context on seasonal itch, see Seasonal Allergies in Dogs.

How Can You Prevent Skin Problems in May?

Start or confirm flea prevention now. Treat every dog and cat in the household on schedule, and do not stop in autumn. Gaps in prevention are the most common reason flea allergy recurs.

Treat the environment. Vacuum carpets and furniture several times a week and wash pet bedding in hot water to remove eggs and larvae.

Rinse after grass exposure. Wipe paws and belly after walks through long grass, and dry between the toes.

Check for grass awns. After walks, inspect between toes, inside ears, and around the eyes.

Manage sun exposure. Provide shade, avoid midday sunbathing, and ask your veterinarian about dog-safe sunscreen for pink noses and bellies.

Bathe on a schedule. Weekly bathing during peak allergy season reduces allergen load on the skin, and medicated baths may be recommended when infection is present.

Keep a symptom log. Noting where and when itch appears helps your veterinarian separate flea, grass, and food triggers. Last month's guide, April Dog Skin Care, covers the early pollen season leading into May.

40 to 50

eggs per day can be laid by a single adult female flea, which is why prevention must be in place before summer (Rust & Dryden, 1997)

May Skin Care Checklist

✓Confirm flea prevention is current for every pet in the home
✓Vacuum and wash bedding weekly to remove flea eggs and larvae
✓Wipe and dry paws and belly after walks through grass
✓Check toes, ears, and eyes for grass awns after outdoor time
✓Protect pink noses and bellies from midday sun

⚠️ Important: Never use permethrin-containing dog flea products on or near cats. Permethrin is highly toxic to cats, and households with both species should ask a veterinarian which products are safe for each pet.

Chlorhexidine Shampoo

Chlorhexidine Shampoo combines chlorhexidine gluconate 2% with ketoconazole 1% to help clear the secondary bacterial and yeast overgrowth that follows flea bites and grass allergy itch.

View Chlorhexidine Shampoo

Not sure what's affecting your dog's skin?

Use our free Dog Skin Condition Checker to identify symptoms, compare conditions, and learn when to see a vet.

Try the Skin Condition Checker

Frequently Asked Questions

When does flea season start for dogs?

In most temperate regions flea activity rises sharply in late spring, usually around May, once temperatures stay between about 21 and 30°C (70 to 85°F). In warm climates fleas are active year-round.

How can I tell if my dog's itching is fleas or grass allergies?

Flea allergy usually causes biting at the lower back and tail base, while grass allergy causes paw licking and itching of the face, armpits, and belly. Finding flea dirt with a flea comb supports fleas.

Can dogs get sunburned?

Yes. Dogs with pink skin and thin hair, especially on the nose and belly, can develop solar dermatitis. Repeated sun damage raises the risk of actinic keratosis and skin cancer in predisposed breeds.

How long should medicated shampoo stay on my dog?

Most veterinary dermatologists recommend 5 to 10 minutes of contact time before rinsing so the active ingredients can work on the skin surface.

Sources

Rust MK, Dryden MW. The biology, ecology, and management of the cat flea. Annual Review of Entomology. 1997;42:451-473.
Dryden MW. Flea and tick control in the 21st century: challenges and opportunities. Veterinary Dermatology. 2009;20(5-6):435-440.
Bruet V, Bourdeau PJ, Roussel A, Imparato L, Desfontis JC. Characterization of pruritus in canine atopic dermatitis, flea bite hypersensitivity and flea infestation and its role in diagnosis. Veterinary Dermatology. 2012;23(6):487-e93.
Hillier A, Lloyd DH, Weese JS, et al. Guidelines for the diagnosis and antimicrobial therapy of canine superficial bacterial folliculitis (Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases). Veterinary Dermatology. 2014;25(3):163-e43.
Hensel P, Santoro D, Favrot C, Hill P, Griffin C. Canine atopic dermatitis: detailed guidelines for diagnosis and allergen identification. BMC Veterinary Research. 2015;11:196.
Olivry T, DeBoer DJ, Favrot C, et al. Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on Allergic Diseases of Animals (ICADA). BMC Veterinary Research. 2015;11:210.
Mueller RS, Bergvall K, Bensignor E, Bond R. A review of topical therapy for skin infections with bacteria and yeast. Veterinary Dermatology. 2012;23(4):330-e62.