Genesis Defense Thermique
A lightweight leave-in blow-dry primer that hydrates, heat protects, strengthens, and helps reduce breakage for weakened hair.
A strong styling-prep product for people with weakened hair who use heat tools and want more protection without a heavy leave-in cream.
People who use the Genesis Serum Fortifiant on their scalp and see results want a lengths-focused equivalent that extends the same anti-breakage philosophy into their daily styling routine. Defense Thermique bridges the scalp serum and the styling step — it makes the whole Genesis system feel cohesive from root to tip.
Applied to towel-dried lengths before blow-drying — after the scalp serum (Genesis Serum Fortifiant) has been applied and before styling. It is the lengths-focused complement to the scalp serum in the Genesis system.
People who blow-dry or heat-style frequently and want their pre-styling step to actively contribute to the Genesis anti-breakage routine. Particularly useful for colour-treated or chemically processed hair.
When layered on top of multiple other leave-in products — defense thermique works best as the primary leave-in before blow-drying, not as an addition to an already loaded product stack.
If hair starts feeling product-heavy or buildup-like after several uses, do a clarifying wash and reset. The defense thermique works best when used alone as the pre-styling leave-in rather than layered with other leave-in products.
- The Genesis Serum Fortifiant on the scalp as the complementary leave-in scalp step
- The Genesis shampoo and conditioner as the wash base for a fully coordinated Genesis routine
- A clarifying shampoo once a week to reset any buildup from daily leave-in use before heavy heat styling
Best For
- Weakened hair
- Breakage-prone hair
- Blow-dry routines
- Heat protection
- Lightweight leave-in support
How to Use
Apply to towel-dried lengths before blow-drying or heat styling. Focus on the mid-lengths and ends. Style as normal.
Key Ingredients
Amino acids draw moisture to the skin (humectant function), replenish the natural moisturizing factors found in healthy skin cells, and provide the raw materials for collagen and elastin synthesis. In the skin's natural state, free amino acids make up a significant portion of the NMF complex that keeps the stratum corneum soft and hydrated.
Draws moisture to the skin, helps maintain hydration, and reinforces the skin barrier.
Attracts and retains moisture, soothes irritated skin, supports barrier repair, and improves skin texture and softness.
Fragrance has no skincare function — it is added purely for sensory appeal and brand experience. Some fragrant ingredients (like linalool, limonene, and eugenol) are known sensitizers that can cause contact dermatitis in sensitive individuals over repeated exposure.
Ingredients to Note
May be a concern for some skin types. Tap to learn more.
Full Ingredient List
About This Product
Kérastase Genesis Defense Thermique sits within the Genesis line — the collection engineered around breakage-related hair fall rather than scalp-driven shedding. Where the Genesis Serum Fortifiant is a scalp-applied daily serum, Defense Thermique is the lengths-focused, pre-styling counterpart. It functions as a leave-in blow-dry primer: applied to towel-dried hair before heat styling, it delivers heat protection alongside the Genesis anti-breakage actives. The "Thermique" designation signals heat-activated performance — the formula is designed to activate and reinforce its protective and fortifying properties when exposed to the heat of a blow-dryer or styling tool. This makes it particularly relevant for heat-styling-heavy users, where mechanical and thermal stress are the primary drivers of the breakage and hairfall the Genesis line is designed to address. It is lighter than a traditional leave-in conditioner cream — more of a spray primer than a coating treatment — which means it can be used daily without buildup concerns.